Home / Statistical Tools / Control Charts / CUSUM / Options
Options¶
This page covers what is specific to the CUSUM Chart dialog. The parts shared by every control chart, the Data Selection window, the Data tab, how subgroups are formed, and the analysis pane, are described once on Create Control Charts. What each option means statistically is on the Math Details page.
The Dialog¶
The dialog is titled CUSUM Chart. There is no variant selector above the tabs: this ribbon entry always draws the same thing, one chart carrying both one-sided sums.
CUSUM has three tabs, not four: Data, Limits & Estimation, and Rules & Display. There is no Capability tab, and this is not simply a hidden tab. The capability calculation and the histogram are switched off for this chart, so there is no specification limit, no target for capability, no capability index, and no histogram anywhere in the output. The Target (optional): box on the Limits & Estimation tab is a CUSUM parameter and has nothing to do with a capability target.
Two controls that appear on the other variable charts are absent from this dialog rather than greyed out:
- The sigma multiplier row. There is no Number of standard deviations (k): box, because the decision interval takes its place. This matters when you read the rest of this page and the Math Details page: with that row gone, the letter k on a CUSUM chart always means the allowance.
- The zone line checkbox. See the Rules and Display tab below.
Data Tab¶
The slot lists are Measurement Columns, X-Axis Labels (Optional), and the Subgroups group with its subgroup mode buttons and identifier drop-down. See Create Control Charts for what each one does.
Two things are specific to CUSUM:
- Under Constant size: the lowest
nthe box accepts is 1, not 2. This is the difference between CUSUM and the subgroup charts on this tab. A value below 1 snaps back with no message. - A constant size of 1 changes the Limits & Estimation tab while you watch. The whole Estimate Sigma group is replaced: the three subgroup methods disappear and the three individual-observation methods appear in their place, together with the moving range length box and the Nelson correction checkbox. Setting the size back to 2 or more swaps them back. Nothing announces the swap.
Subgroup ID column: and Subgroups across columns can both produce subgroups of unequal size, because an identifier can repeat a different number of times and a row can have blanks in some of the checked columns. Unequal sizes are supported: the decision interval then steps from point to point instead of running straight, because it is a multiple of the standard error at that point.
Limits and Estimation Tab¶
This tab carries seven groups: Estimate Sigma, Transformation, CUSUM Parameters, and Historical Values on the left, and Control Limits, Estimate Limits From, and Split Control Limits on the right.
Control limits¶
The Control Limits group on the Limits & Estimation tab sets how the limits on every panel are obtained.
| Control | Type | Default | What it does |
|---|---|---|---|
| Shewhart | radio button | selected | The center line and the limits are computed from the data. |
| Manual | radio button | not selected | You type the limits yourself, one row per panel. |
| None | radio button | not selected | No limits are drawn. The points, the center line, the process statistics, and the outlier markers are all still produced. |
Manual is not offered on every chart and can be switched off by settings on other tabs. The availability table below covers both.
Choosing None also turns the out-of-control tests off. On a variable chart, blanking the limits blanks every test result as well, so no point is flagged, including by the tests that need only the center line. The zone lines checkbox is not greyed out when you choose None, but ticking it has no visible effect because there are no zone values to show.
Validation: none of the three radios can produce an invalid state, so there is no message.
Math: Control Limits and Zones.
On CUSUM the group holds Shewhart and None only. The Manual radio is not shown, and neither is the sigma multiplier box that normally sits under these radios.
Manual limits are not offered on this chart¶
There is no Manual radio and no grid of UCL, Center, and LCL boxes. Typed limits are rejected for the time weighted charts, so the option is removed from the dialog rather than left to fail later. If a saved analysis is reopened with Manual stored in it from somewhere else, the selection is quietly returned to Shewhart.
Historical (known) values¶
The Historical Values group lets you supply a number instead of estimating it, so the limits describe a process you have already characterized rather than the data in front of you. Every box is a text box, every box starts blank, and blank means estimate it from the data.
| Control | Type | Default | What it replaces |
|---|---|---|---|
| Mean: | text box | blank | the mean behind the center line |
| Standard deviation (overall): | text box | blank | the overall sigma |
| Standard deviation (within): | text box | blank | the within-subgroup sigma |
| Mean (between): | text box | blank | the mean of the subgroup means |
| Standard deviation (between): | text box | blank | the between-subgroup sigma |
Which boxes appear depends on the chart, because a box for a quantity the chart never uses would be misleading.
| Chart | Boxes shown |
|---|---|
| Xbar-R, Xbar-S, I-MR | Mean, overall, within |
| I-MR-R/S | all five |
| EWMA, CUSUM | Mean, within |
| Levey-Jennings | Mean, overall |
Behavior worth knowing:
- A supplied value wins, and it is applied last. The estimate is computed from the data first and then overwritten, so a First N baseline still selects which points fed the discarded estimate, and still governs anything you did not supply.
- One number can change two. Supplying a within sigma also redefines the between sigma, and supplying a between sigma redefines the sigma of the subgroup means, because the remaining quantity is back-solved from the data.
- A supplied sigma carries no degrees of freedom, so it gets no confidence interval in the capability output. A supplied mean affects no degrees of freedom.
- One value covers every phase. With split control limits on, the same supplied number applies to all phases; there is no per-phase historical value.
- A transformation discards them for that run. Turning on Box-Cox or Johnson greys out the whole group and the values are not used. What you typed reappears if you turn the transformation off.
Validation: none of these boxes is range-checked in the dialog. The one engine check is on Levey-Jennings, which refuses a supplied overall standard deviation that is not a positive number. Anywhere else an unusable value is accepted and shows up as an unusable chart.
Math: Process Sigma Estimation.
On CUSUM the group shows two boxes, Mean: and Standard deviation (within):. The overall standard deviation box is not shown, because this chart reads the within estimate only and an overall box would do nothing.
What switches these options off¶
Four combinations of settings make an option on this tab unavailable. Every one of them acts the moment you type or select, and none of them shows a message, so it is worth knowing them before you go looking for a control that has greyed out.
| When this is set | This becomes unavailable |
|---|---|
| A Box-Cox or Johnson transformation | Manual limits. The radio greys out, and a Manual selection reverts to Shewhart. The Historical Values boxes are also ignored for that run. |
| Any split mode other than None, whether or not you have entered break points yet | Manual limits, in the same way. Selecting the mode is enough; the gate does not check whether the split produces anything. |
| A lower or upper specification limit on the Capability tab. A target alone does not do this. | First N subgroups under Estimate Limits From. The selection reverts to All subgroups. Levey-Jennings, EWMA, CUSUM and Z-MR have no Capability tab, so this gate cannot arise on them. |
| A transformation and a specification limit together | Split control limits. The whole Split Control Limits group greys out and the mode reverts to None. |
The specification-limit gate reads the two specification boxes only, so a Target: on its own leaves First N subgroups: selectable. That combination does not produce a chart: a target alone is enough to turn the capability calculation on, and the engine refuses to combine capability with a First N baseline, so the run stops with "Capability cannot be combined with a First-N baseline." Clear the target, or return Estimate Limits From to All subgroups.
Two chart-level rules sit alongside them: EWMA and CUSUM never offer manual limits at all, and Levey-Jennings treats manual limits and historical values as mutually exclusive, so entering either one greys out the other.
What Estimate Limits From (Baseline Estimation) does¶
It changes what the limits are estimated from. It never changes what is plotted. Every point always appears on the chart. Asking for the first 25 subgroups does not hide subgroup 26 onward. It means the center line and the control limits are computed from the first 25 subgroups and then drawn straight across the whole chart, so the later points are judged against the earlier baseline. That is the entire purpose of the setting: it is how you freeze a known-good period and watch what happens afterwards.
The same setting carries two labels. It is Estimate Limits From on the variable charts and Baseline Estimation on the attribute and rare-event charts, because those dialogs were written separately. The intent is identical, but the smallest count you may enter differs, and so do a few of the edge cases, so use the block written for this chart.
| Estimated from the selected points only | Computed from all the points regardless |
|---|---|
| The mean behind the center line | Every plotted value |
| The overall sigma | Each subgroup's own mean, range, and standard deviation |
| The within-subgroup sigma and everything it is built from | The minimum, the maximum, and the count |
| The between-subgroup sigma | The observed parts per million outside the specification |
| The moving-range estimates on an individuals chart | The histogram and the distribution fit |
| The estimated proportion or rate on an attribute chart | The out-of-control tests, which are applied to every point |
| The reported degrees of freedom | |
| The transformation itself |
Two of those rows surprise people:
- The transformation is fitted on the baseline too. A Box-Cox lambda or a set of Johnson parameters is fitted from the baseline points only and then applied to every row in the data. Change the baseline and you change the transformation, not just the limits.
- The degrees of freedom come from the baseline, so a short baseline widens the capability confidence intervals as well as changing the limits.
With split control limits on there is still only one count. It is reused inside every phase, capped at the length of that phase, so a phase shorter than the count simply uses all of its own points. The count never reaches across a phase boundary, and there is no way to give one phase a different baseline from another.
Math: Baseline and Limit Estimation.
Estimate Limits From¶
| Control | Type | Default | Accepts |
|---|---|---|---|
| All subgroups | radio button | selected | |
| First N subgroups: | radio button | not selected | |
| the count box beside it | text box | blank | a whole number of 5 or more. Its tooltip reads "Minimum 5 subgroups". |
The count is in plotted points, not in worksheet rows. On an individuals chart it counts points, and the moving ranges available inside that window are one fewer than the count at the default moving range length, fewer still if there are gaps.
Everything this control does when your entry is not usable, it does silently:
| What you do | What happens |
|---|---|
| Select First N subgroups: and leave the box blank | Exactly the same as All subgroups: every point estimates the limits. |
| Type a number below 5 | Raised to 5 as soon as the box loses focus. |
| Type a number larger than the data | Every point is used. |
| Leave a blank subgroup inside the window | It does not use up one of the N. The window reaches further into the data to find real subgroups. |
| Exclude a point as an outlier inside the window | The same: it does not use up one of the N. |
A specification limit switches this off. Type a lower or an upper specification limit on the Capability tab and First N subgroups: greys out and the selection reverts to All subgroups, because a frozen baseline and a capability calculation disagree about which data describes the process. Levey-Jennings, EWMA, CUSUM and Z-MR have no Capability tab, so this cannot arise on them. There is no message, and clearing the specification limit makes the radio available again.
A target on its own does not switch it off, and the combination then fails
The dialog gate reads the LSL: and USL: boxes only, so a Target: with both specification boxes empty leaves First N subgroups: selectable. It should not be. A target on its own is enough to turn the capability calculation on, and the engine refuses to combine any capability calculation with a First N baseline, so pressing Finish in that state produces no chart at all and the message "Capability cannot be combined with a First-N baseline."
To avoid it, either clear the Target: box or set Estimate Limits From back to All subgroups.
Every phase still needs at least five usable points. With split control limits on, one phase too short fails the whole analysis with a message instead of a chart, whatever this setting says.
Validation: nothing about this control is ever reported. The count is corrected in place and the analysis runs.
On CUSUM the count is a count of plotted points. With a subgroup size of 5, First N subgroups: 25 estimates from the first 125 rows; with a subgroup size of 1 it estimates from the first 25 rows, even though the label still reads "subgroups". The specification-limit gate described above cannot arise here, because CUSUM has no Capability tab.
Estimate Sigma, subgrouped data¶
The Estimate Sigma group chooses how the process standard deviation behind the limits is estimated. The estimates differ in how they weight the subgroups and in how much they are disturbed by an unusual one, not in what they are trying to measure.
| Control | Type | Default | What it uses |
|---|---|---|---|
| Rbar (average range) | radio button | selected when it is the first method offered | the ranges of the subgroups |
| Sbar (average standard deviation) | radio button | selected when it is the first method offered | the standard deviations of the subgroups |
| Pooled standard deviation | radio button | not selected | all the within-subgroup variation pooled together |
Each dialog shows only the methods that suit its chart, and the first one shown is the one selected when the dialog opens.
| Chart | Methods offered | Default |
|---|---|---|
| Xbar-R | Rbar, Pooled standard deviation | Rbar |
| Xbar-S | Sbar, Pooled standard deviation | Sbar |
| I-MR-R/S | Rbar, Sbar, Pooled standard deviation | Rbar |
| EWMA, CUSUM | all three, when the data is subgrouped | Rbar |
If the data turns out not to be subgrouped, for example because a subgroup identifier column has a different value on every row, no subgroup method can be evaluated and a moving-range estimate is used instead, whatever the radio buttons show. No message is given.
Validation: this is a closed set of radio buttons, so there is nothing to validate and no message.
Math: Process Sigma Estimation.
With a subgroup size of 2 or more, CUSUM offers all three: Rbar (average range), selected when the dialog opens, Sbar (average standard deviation), and Pooled standard deviation.
Estimate Sigma, individual observations¶
With one observation per point there is no within-subgroup spread to work with, so the estimate comes from how much consecutive points differ.
| Control | Type | Default | What it uses |
|---|---|---|---|
| Average moving range | radio button | selected | the mean of the moving ranges |
| Median moving range | radio button | not selected | the median of the moving ranges, which is much less disturbed by one large jump |
| Square root of MSSD | radio button | not selected, and shown only on the charts that offer it | the mean of the squared successive differences |
| Moving range length: | text box | 2 | a whole number from 2 to 100 |
| Use Nelson moving-range correction | check box | unchecked | on or off |
Moving range length is how many consecutive points each moving range spans. It disappears when Square root of MSSD is selected, because that method always uses consecutive pairs and would ignore it. It is shown only on the dialogs that offer the individuals sigma methods; a subgrouped chart that uses a moving range internally does not expose it, and its length is fixed at 2.
Use Nelson moving-range correction repeatedly removes unusually large moving ranges before averaging them, so that a genuine upset does not inflate the limits that are meant to detect it. It is available only with Average moving range: choose another method and the tick is cleared without a message, and the checkbox greys out. It considers only the moving ranges inside the baseline window, so a First N baseline restricts it further.
Validation: a moving range length below 2 or above 100 is silently replaced by the nearest allowed value, and the box shows the corrected number. There is no message.
Math: Process Sigma Estimation and Moving Ranges.
With a subgroup size of 1, CUSUM offers all three individual-observation methods, Average moving range (selected), Median moving range, and Square root of MSSD, with the moving range length box and the Nelson correction checkbox beside them.
Where the sigma choice changes more than the sigma¶
Three of these interactions change the dialog or the chart itself, not only the number behind the limits.
- A subgroup size of one swaps the whole group. On EWMA and CUSUM, setting a constant subgroup size of 1 on the Data tab replaces the three subgroup methods with the three individual-observation methods and adds the moving range length and the Nelson checkbox. Setting it back to 2 or more swaps them back. Nothing warns you that the group you were looking at has been replaced.
- On I-MR-R/S the sigma choice decides which chart the third panel is. Choosing Rbar or the pooled standard deviation draws a range chart there; choosing Sbar draws a standard deviation chart instead. The row name in the manual limits grid does not change with it, so the grid still names both.
- Levey-Jennings has no Estimate Sigma group at all. Its limits come from the overall standard deviation of the data, which is the main thing separating it from an Individuals chart, so there is no method to choose and the unbiased-constants checkboxes are not shown either.
Math: Process Sigma Estimation.
The unbiased-constants checkboxes¶
Every estimate of a standard deviation from small samples runs slightly low on average. These two checkboxes decide whether that small bias is corrected. They have different defaults, which is easy to miss.
| Control | Type | Default | What it changes |
|---|---|---|---|
| Use unbiased constants (within sigma) | check box | checked | the correction applied to the within-subgroup estimate |
| Use unbiased constants (overall sigma) | check box | unchecked | the correction applied to the overall estimate |
The within checkbox greys out for some methods, because it would do nothing. It has an effect only with Sbar, with the Pooled standard deviation, and with the Square root of MSSD. With Rbar, the Average moving range, and the Median moving range the correction is always part of the estimate, so the dialog disables the checkbox rather than pretending the choice exists.
The overall checkbox is never greyed out, and it is a small correction because it is applied over the whole data set. It never moves a drawn control limit on any chart: the one chart whose limits come from the overall estimate is Levey-Jennings, and that chart shows neither checkbox.
Levey-Jennings does not show either box, and ignores both. Its overall standard deviation is always the uncorrected form.
Validation: checkboxes cannot be invalid, so there is no message. When a correction factor does not exist for the size it would be evaluated at, the correction is skipped and the uncorrected value is reported rather than nothing.
Math: Process Sigma Estimation and Control Chart Constants.
On CUSUM the within checkbox is disabled under Rbar and under the two moving range methods, which are the defaults on each side of the subgroup size switch, and becomes live under Sbar, under the pooled standard deviation, and under the square root of MSSD. It changes the estimate itself, which moves both the decision interval and the allowance, because both are multiples of that estimate. This chart has no standard deviation panel, so the checkbox never moves a center line.
CUSUM Parameters¶
This group exists on no other chart. It sets the two numbers that decide how the sums accumulate and when they signal, plus the two options that change how an accumulation starts.
| Label as shown | Control | Default | Accepts | What it does |
|---|---|---|---|---|
| Allowance (k): | text box, with the hint "Default 0.5" under it | 0.5 | any finite number greater than zero | How much of a deviation is absorbed before anything is accumulated, measured in standard deviations of the plotted value. |
| Decision interval (h): | text box, with the hint "Default 4.0" under it | 4.0 | any finite number greater than zero | How far a sum has to travel before the point signals, measured in the same units. It is the limit drawn on the chart. |
| Target (optional): | text box, with the hint "Blank = center on the section mean" under it | blank | any finite number, or blank | The value the deviations are measured from. Blank means the chart centers itself on the mean. |
| Use fast initial response (FIR) | check box | unchecked | on or off | Starts each sum at a head start instead of at zero. |
| Headstart: | text box, with the hint "Default 2.0" under it | 2.0 | zero or any finite number greater than zero | The size of that head start, measured in standard deviations. |
| Reset accumulation after a signal | check box | unchecked | on or off | Starts the accumulation again at the point after a signal instead of carrying the total forward. |
Allowance and decision interval are both in sigma units. Neither is in the units of your measurement. Each is multiplied by the standard deviation of the plotted value at that point, so both scale with the process and, on subgrouped data, with each subgroup's own size.
Target changes what the chart is monitoring. With the box blank the chart asks whether the process has drifted away from its own average. With a value in it the chart asks whether the process has drifted away from that value, and a process that is stable but off target accumulates steadily from the first point. On a split chart the one target you type applies to every phase, while a blank target lets each phase center on its own mean.
Headstart is editable only while FIR is checked. Both the label and the box are greyed out with the checkbox cleared, and the value you typed is kept and comes back when you tick it again. With FIR off, every sum starts at zero.
What the head start actually does. It is the starting value of the accumulation, applied at the first plotted point and, when Reset accumulation after a signal is also on, again at the first plotted point after each signal. It is re-evaluated in the standard deviation of the point it is applied at, so a change of subgroup size scales it. A head start of 0 is accepted and is the same as leaving FIR off.
What reset does, and what it costs. Without it, a sum that has crossed the decision interval stays above it, so every point after the first signal signals as well until the deviations pull the sum back down. With it, the sum restarts at the head start (or at zero when FIR is off) at the next plotted point, so a single event produces a single signal. Nothing is removed from the chart either way: the point that signalled is still drawn at the value it reached.
Validation: none of these boxes reports anything. A blank, non-numeric, zero, or negative entry in Allowance (k): or Decision interval (h):, and a blank, non-numeric, or negative entry in Headstart:, is discarded and the box snaps back to the value it held before, with no message. A non-numeric entry in Target (optional): snaps back the same way, while clearing the box is legal and means center on the mean.
Transformation¶
A transformation replaces each measurement with a rescaled version of itself, chosen so the rescaled values sit closer to a normal distribution. Control charts assume a normal distribution and never fit any other one, so a transformation is the only remedy the product offers for skewed measurement data on a control chart.
| Charts | Transformation group box |
|---|---|
| Xbar-R, Xbar-S, I-MR, I-MR-R/S, EWMA, CUSUM | Offered |
| Levey-Jennings, Z-MR | Not offered. There is no control, and no transformation is applied. |
| p, np, Laney P', c, u, Laney U', G, T | Not offered. These charts plot counts, proportions, or waiting times and have their own distributions built in. |
Controls¶
The group box is headed Transformation.
| Label as shown | Control | Default | Valid entries | What it does |
|---|---|---|---|---|
| None | Radio button | Selected | n/a | The chart is built from the measurements as entered. |
| Use Johnson Transformation | Radio button | Not selected | n/a | Fits a Johnson family transformation. |
| Use Box-Cox Transformation | Radio button | Not selected | n/a | Fits a Box-Cox power transformation. All values used must be positive. |
| Use Optimal Lambda | Radio button | Selected as soon as Box-Cox is chosen | n/a | The power is fitted from your data. |
| Enter Custom Value | Radio button | Not selected | n/a | You supply the power instead of fitting it. |
| (lambda box) with the hint (-5 to 5) beside it | Text box, no label of its own | Empty | A number | The power to use. |
Hidden rather than disabled: the Use Optimal Lambda and Enter Custom Value buttons appear only while Use Box-Cox Transformation is selected, and the lambda box and its (-5 to 5) hint appear only while Enter Custom Value is selected. The Johnson transformation takes no parameters, so it reveals nothing.
Validation. The dialog does not check the lambda box against the range in the hint beside it, and it shows no message of any kind. The value you type is passed on as it stands, and the supported range is enforced further in, where the transformation is computed. The two shared math pages define the transformations and the range: Box-Cox Transformation and Johnson Transformation.
What a transformation affects¶
A transformation is not a display option. It changes the numbers the whole analysis is built from, so read the chart in transformed units afterwards.
| Affected | Not affected |
|---|---|
| The plotted points on every panel | Which points appear, and in what order |
| The center line, the control limits, and the zone lines | The rules that are switched on, and their thresholds |
| Every sigma estimate and its degrees of freedom | The sigma multiplier |
| The vertical axis, which is now in transformed units | |
| The values reported in the summary table | |
| Any specification limits, target, and the capability results computed from them |
The transformation is fitted once for the whole chart, and it is fitted on the baseline points only, not on all the data. With splits in effect, the single fit uses the union of the per-phase baseline windows, that is exactly the points that feed each phase's own center line and within-phase sigma, and the fitted transformation is then applied to every row of the chart. Individual phases never get their own transformation. Full detail: Splits and Phases.
Blank rows are handled slightly differently by the two transformations while the fit is being made: Box-Cox keeps a blank as a hole, so the moving range chain breaks in exactly the places it would have broken anyway, while the Johnson transformation drops blanks from the values it fits on.
With a transformation active on a CUSUM chart, everything the accumulation is built from is in transformed units: the plotted value at each point, the center, the estimated standard deviation, and therefore the allowance and the decision interval as well. A Target (optional): you typed is transformed alongside the data, so enter it in the original units. Both the vertical axis and every value in the summary table are in transformed units.
Conditional behavior¶
| Condition | Effect |
|---|---|
| Any transformation is active | Manual control limits become unavailable. The Manual option is greyed out, and if it was already selected it reverts to the calculated limits. Limits typed by hand would be in the original units and there is nothing to convert them with. |
| Any transformation is active | The Historical Values boxes are greyed out, and any value already typed there is dropped for this run rather than converted. The typed text stays in the box and takes effect again when the transformation is switched back to None. |
| A transformation is active and a capability analysis is active | Split Control Limits is greyed out entirely and the split mode reverts to None. A capability analysis counts as active as soon as a lower or upper specification limit is entered. This combination can only arise on the charts that offer both a transformation and a Capability tab. |
| A transformation is active and splits are in effect | One transformation for the whole chart, fitted on the union of the per-phase baseline windows, applied to every row. Both the plotted values and the summary table report transformed results. |
| Estimate Limits From is set to a first-N count | The transformation is fitted from that baseline subset, not from all the data. Changing the count changes the transformation, and therefore changes every plotted value. |
| Box-Cox is selected | The Box-Cox transformation is defined for positive values only. Zero and negative measurements cannot be transformed this way. |
The first row of that table, the one about manual limits, cannot arise on this chart: manual limits are not offered here in the first place.
Split Control Limits¶
A split divides the chart into consecutive sections, called phases, and gives each phase its own center line and its own control limits. Use it when the process changed on a known date: a new supplier, a tooling change, a settings change. The limits then step at the change instead of averaging across it.
Every phase estimates its own center line, its own sigma, its own control limits, and its own zone lines, and the out-of-control run counters restart at every phase boundary. Splitting never hides or moves a point: all points stay on the chart in their original order, and only the limits they are judged against change. For the formulas, and for the full list of what is shared across the chart versus estimated per phase, see Splits and Phases.
Controls, variable chart dialogs¶
The group box is headed Split Control Limits and holds three mutually exclusive mode buttons plus the editors each mode reveals.
| Label as shown | Control | Default | Valid entries | What it does |
|---|---|---|---|---|
| None | Radio button | Selected | n/a | One center line and one set of limits for the whole chart. |
| Split by column | Radio button | Not selected | n/a | A new phase starts at every row where the chosen column's value changes. |
| (split column list) | Drop-down list, no label of its own | Nothing selected | Any one column offered in the list | Names the column whose value changes drive the phases. |
| Manual break points | Radio button | Not selected | n/a | Phases start at the point numbers you type. |
| (break entry box) | Text box, no label of its own. Tool tip: "Enter a 1-based chart point (subgroup) number" | Empty | A whole number from 1 up to the number of plotted points | Holds one break number until you press Add. It is a staging box; typing in it alone changes nothing. |
| Add | Button | n/a | n/a | Moves the typed number into the break list, in ascending order, and inserts a matching label slot. |
| Remove | Button | n/a | n/a | Deletes the break selected in the list and its label slot. |
| (break list) | List box | Empty | n/a | Shows the break point numbers currently in effect. |
| Split Labels (shown beside each divider): | Label above one text box per phase | One empty box, named "Split 1" | Any text | The text drawn beside each divider on the chart. |
Hidden rather than disabled: the split column list appears only while Split by column is selected, and the break entry box, Add, Remove, the break list, and the whole Split Labels block appear only while Manual break points is selected.
Disabled: the entire group box is greyed out, and the mode reverts to None, when a transformation and a capability analysis are both active. See the conditional behavior table below.
Validation, and what it does not tell you. These dialogs have no validation message line in this group box at all. Add silently refuses the entry, leaving it in the box, when it is not a whole number, when it is below 1, when it is at or beyond the known number of plotted points, or when that break is already in the list. Nothing appears on screen in any of those cases. When the point count is not yet known to the dialog the upper check is skipped, so a break past the end of the data can be added and is dealt with later by the calculation. Remove with nothing selected in the list does nothing and says nothing. There is no check at all on how short a phase the break would create.
What a break number means¶
A break number is the 1-based number of the plotted point that starts the new phase, the same number you read along the horizontal axis, not a worksheet row address. On charts plotted from subgroups it is the subgroup number, not the raw data row. On charts where one row is one point the two are the same.
Breaks must be different from each other and are kept in ascending order for you. A break at point 1 does nothing, because the first phase already starts there.
Split Labels¶
The Split Labels (shown beside each divider): block gives one text box per phase, so the number of boxes is always the number of breaks plus one. Each box is named Split 1, Split 2, and so on, in chart order. Those names are slot names, not the labels: they are fixed and cannot be edited. Whatever you type in the box beside a slot is what gets drawn on the chart. Leaving a box empty draws no label for that phase.
Adding a break inserts a new empty box at the position that changed rather than adding one at the end, so labels already typed stay with the phases they were written for.
The block appears only in the manual break mode. There is no way to type phase labels when the phases come from a column: in column mode the label beside each divider is the split column's own cell value.
The split column is claimed from the Data tab¶
The split column is chosen here, but it is one of the worksheet columns listed on the Data tab, and a column can hold only one job at a time. Choosing a column as the split column claims it: on the Data tab that column is greyed out and can no longer be checked as a measurement column, an X-axis label column, a subgroup ID, or a part column. Releasing it here gives it back. A column already claimed for one of those other jobs appears greyed in the split column list and cannot be picked. Neither the greyed check box on the Data tab nor the greyed list entry here explains which job is holding the column.
Selecting the column mode with no column chosen is not an error. It is a deliberate decision in the product, and it means do not split. Nothing is flagged, no message appears, and the chart is built with one set of limits, exactly as if the mode were None. The same is true of the manual break mode with an empty break list.
Minimum phase length, and two opposite outcomes¶
Every phase has to be long enough to estimate limits from. The minimum differs by chart family, and so does what happens when a break breaks the rule.
| Charts | Shortest phase allowed | A break that would create a shorter phase |
|---|---|---|
| Variable charts | 5 points | The whole analysis is rejected and no chart is produced. |
| Attribute and rare-event charts | 2 points | The break is dropped and the chart is built without it. |
That is the same user action with opposite outcomes: on an attribute chart a too-short phase costs you a divider, on a variable chart it costs you the chart.
The variable chart dialogs validate neither number. They do not check the minimum, and they do not check the arithmetic of the phase lengths your breaks imply, so a set of breaks can be accepted without complaint at entry and then fail when the chart is built. The attribute and rare-event dialogs do check the two-point rule as each break is added, with the message shown above.
A variable chart phase also fails the analysis when it holds fewer than five values that are actually present, even when the phase itself is long enough. Blank rows inside a phase therefore matter as much as its length.
On CUSUM the five-point minimum is five plotted points, and the dialog does not check it, so a break that leaves a phase of four points is accepted here and then stops the analysis with a message instead of producing a chart.
Conditional behavior¶
| Condition | Effect |
|---|---|
| Any split mode other than None is selected, on a variable chart | Manual control limits become unavailable. The Manual option is greyed out, and if it was already selected it reverts to the calculated limits. |
| A split mode is selected but produces no phases (column mode with no column, or manual mode with an empty list), on a variable chart | Manual control limits are still unavailable. The check looks at which mode button is selected, not at whether any phase boundary results. Setting the mode back to None restores the Manual option. |
| Any split mode selected, on an attribute or rare-event chart | No such restriction. Manual limits stay available, and the band you enter is drawn in every phase. |
| A transformation and a capability analysis are both active | The whole Split Control Limits group box is greyed out and the mode reverts to None. A capability analysis counts as active as soon as a lower or upper specification limit is entered. This can only arise on the charts that offer both a transformation and a Capability tab. |
| A transformation is active, with or without splits | One transformation is fitted for the whole chart and then applied to every row. Phases never get their own transformation. |
| Estimate Limits From, or Baseline Estimation, is set to a first-N count | There is one count for the whole chart. It is reused inside every phase and capped at that phase's length, so a short phase uses all of its own points while a longer phase in the same chart uses the count you typed. There is no per-phase count, and the count never reaches across a phase boundary. See Baseline and Limit Estimation. |
| Out-of-control rules are on | Every run and every window restarts at each phase boundary. A run in progress when a boundary arrives is abandoned, so a run of eight points that straddles a boundary cannot combine into one signal. The point-by-point test against the limits is unaffected, because each point is compared with its own phase's limits. |
| A historical mean or sigma is supplied | The one value you supply is applied to every phase. It is not a per-phase entry. |
Splits are edited after the fact in the Control Chart task pane as well, but only the manual break points and the labels. The column mode cannot be selected or cleared there.
One effect of splitting is specific to this chart: the accumulation restarts at every phase boundary. Both sums go back to their starting value at the first point of each phase, and the head start is applied again there when FIR is on. A drift that was building up at the end of one phase does not carry into the next.
Rules and Display Tab¶
Out-of-Control Rules¶
The group box headed Out-of-Control Rules holds one row per rule. Each row is a check box carrying the rule's description, followed by up to two small numbered boxes labelled N = and M =. N is how many points the rule needs, and M, where a rule has one, is the length of the window those points must fall inside.
Ticking a rule adds its test to the analysis. Nothing else about the chart changes: the center line, the limits, and the plotted points are the same whether a rule is on or off.
Thresholds. Every box arrives pre-filled with that rule's standard value rather than blank, so you can see what the rule will do before you change it. Clearing a box means use the standard value; it does not mean zero. Unticking a rule leaves its numbers visible but locks the boxes, so the value you set is still there when you tick the rule again.
There is no message when a threshold is refused. On the attribute and rare-event dialogs a count below 2 is silently raised to 2 as soon as you leave the box. On the variable chart dialogs a value that is blank, zero, or negative is treated as the standard value.
The rule set on EWMA and CUSUM¶
These two charts offer Rule 1 only. The group box holds a single row, Rule 1 - Beyond K sigma from center, and it is ticked by default. No other rule has a row, and none can be turned on.
The reason is what these charts plot. Each point already carries the influence of the points before it, so the run and trend patterns the other rules look for are no longer independent evidence of anything.
Clearing Rule 1 does not switch the test off on this chart
On a CUSUM chart the out-of-control detector that the other charts use is never invoked. A point is flagged directly by the accumulation test itself, at the moment the sum is found to exceed the decision interval, and that test does not read the checkbox. So clearing the Rule 1 box leaves the box cleared and the flagging unchanged: points beyond the decision interval are still marked, and they are still counted in the OOC points row of the summary table.
If you do not want the markers drawn, clear Show out-of-control indicators in the Analysis Pane, which hides them on the finished chart.
Conditional behavior¶
| Condition | Effect |
|---|---|
| Control limits set to None, on a variable chart | No rule fires. Every rule result is cleared along with the limits, so no point is marked even though the rules are still ticked. |
| Control limits set to None, on an attribute or rare-event chart | The center line is still estimated, so rules 2, 3, and 4, and Rule 9 on a G chart, still fire and still mark points. Rule 1 cannot fire, because there are no limits to exceed. |
| Control limits set to Manual | The rules run against the band you entered, and the zone lines are derived from that band. |
| Manual limits entered with the center left blank, on an attribute chart | There is no center line and no zone lines, so rules 2, 3, and 4 cannot fire. |
| Splits are in effect | Every run and every window restarts at each phase boundary. A run in progress when a boundary arrives is abandoned and cannot combine with the run that starts after it. |
| A point is blank or excluded | Runs break at the gap rather than bridging it. For the two window rules, rules 5 and 6, a blank invalidates every window that overlaps it, not just the run. |
| A rule is unticked | Its threshold value is kept and its box is locked. Nothing is lost by turning a rule off and on again. |
| The sigma multiplier is changed, on a variable chart | The zone lines move with the band, because they are placed at thirds of it. At a multiplier other than 3 the line labelled 2 sigma is not at 2 sigma, which changes what rules 5 through 8 test. On the attribute charts and Z-MR the zone lines are at a true 1 and 2 sigma at any multiplier. |
| A capability analysis or a transformation is active | Neither affects the rules. The rule set, the thresholds, and the panels checked are the same. |
Background reading for your operators: Out-of-Control tests.
Three rows of that table cannot arise on a CUSUM chart, because the controls they describe are not in this dialog: there is no Manual limit type, there is no sigma multiplier to change, and there are no zone lines for a multiplier to move.
Both sums are tested. The upper series and the lower series are each checked against their own limit, so the OOC points row of the summary table is reported separately for Upper CUSUM (C+) and Lower CUSUM (C-).
The chart marks a point, it does not name a cause. A point that signalled is drawn in a different color and counted in the summary table, and that is the whole of the report. Since only one test exists on this chart, a marked point always means the same thing: that sum went past the decision interval.
Display Options¶
The Display Options group box on this tab holds the reference line editor. On the other variable charts it also holds the zone line checkbox; on this one it does not.
This chart has no sigma zones, so the dialog does not show a zone line checkbox at all. The Analysis Pane does show one, where it has nothing to act on.
Reference lines¶
A reference line is a horizontal line at a Y value you supply: a specification limit, a target, a contract threshold, anything you want the points compared against. Until you add one the editor reads "No reference lines configured. Use the row editor below to add Y-value reference lines."
Each reference line is one row with four editable cells and a remove button:
| Cell | What it sets | Default |
|---|---|---|
| Value | the Y position of the line | 0 |
| Label | the legend entry for the line | blank |
| Color | the line color, picked from a color button | red |
| Thickness | the line weight, chosen from 0.5, 1.0, 1.5, and 2.0 | 1.0 |
| X | removes that row. Its tooltip reads "Remove this reference line" | n/a |
Value is not validated. Type something that is not a number and the cell keeps the value it had. A blank Label keeps the line out of the chart legend; the line is still drawn, under a generated name built from its value. The editor scrolls on its own once the list of rows is taller than the space allowed for it.
- Add Reference Line: appends a blank row and refreshes the chart preview by itself. Removing a row with its X button does the same.
- Apply: commits edits to Value, Label, Color, and Thickness, which do not refresh the preview on their own. Its tooltip reads "Refresh the chart preview to reflect any pending reference-line edits". The button appears only once at least one reference line exists, and does nothing when there is nothing outstanding to commit.
So adding and removing lines is immediate, while editing an existing line needs Apply.
Reference lines are drawn on the location panel only
Reference lines appear on the panel that plots the measurement itself: the Xbar panel, the Individuals panel, the EWMA panel, or the Z panel of a Z-MR chart. The dispersion panels (Range, Standard Deviation, Moving Range) are in different units, so they never carry reference lines. The location panel's Y axis is stretched to include every reference line value, so a line outside the data still shows.
This has a consequence on the single-panel dispersion charts. R only, S only, and Moving Range only draw no location panel, so a reference line entered in the editor never appears anywhere on the chart. The editor still accepts it and still lists it. If you need a reference line against a range or a standard deviation, there is no dialog option that will draw one.
CUSUM is the exception: it is a single overlay chart rather than stacked panels, and it draws reference lines on that chart.
A reference line on a CUSUM chart is drawn at a value of the accumulated sum, not of your measurement, so a specification limit entered here is not meaningful. The vertical axis is stretched to include every reference line you add.
Layout you do not choose¶
Nothing else about the appearance of the chart is a dialog option. These are fixed:
- One chart, not two panels. Both sums are always computed and both are always drawn, on one chart, with a shared center line at zero and mirror-image limits. There is no option to suppress a side.
- The chart title is CUSUM Chart, extended with the group and the measurement column name when those exist.
- The axes. The X axis is numbered by plotted point and titled Subgroup; the Y axis is titled Cumulative Sum and is scaled to fit both sums, both limits, and any reference lines.
- The legend sits on the right and names the series that were drawn: C+, C-, UCL, LCL, and Center.
Once the chart exists, reference lines cannot be changed from the Analysis Pane: to add, edit, or remove one you modify the analysis and run it again.
Task Pane¶
The Control Chart pane is the same on every chart and is described on Create Control Charts. On a CUSUM sheet it binds to the worksheet named CUSUM.
Show zone lines does nothing on this chart
A CUSUM chart has no sigma zones and none are drawn, so the pane's Show zone lines checkbox has nothing to show or hide. The checkbox stays available and ticking it changes nothing on the chart.
Apply Splits re-runs the whole analysis, so it re-runs the accumulation as well, with the new phase boundaries restarting both sums.