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Type 1 MSA¶

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QXL Stat Tools Tab > MSA (Gage R&R) > Type 1 Gage Study (Repeatability Only)

Data source¶

Measure one part at least 25 times. Enter these measurements into a single column in Excel.

Specification Limits: Enter the Upper Specification Limit (USL) and/or Lower Specification Limit (LSL) if available. Alternatively, you can enter the value of (USL-LSL) under Tolerance. For example: if LSL = 10 and USL = 13, you could enter Tolerance = 3.

Percentage of Tolerance: Enter the percent of tolerance for use in the study. The default is 20%. See math for Cgk below.

Number of Standard Deviations: Enter the number of standard deviations to be used in the study. The default is 6. See math for Cg below.

Reference Value: Enter the true value for the part being measured (optional).

Results¶

Bias¶

If the reference value is provided, Quantum XL will calculate the Bias and the associated T statistic and p-value.

The T and p-value represent the results from a one sample t-Test. If the p-value is less than .05, then you can be at least 95% confident that the bias is non-zero.

Type 1 Bias

Cg and Cgk¶

Ideally, both Cg and Cgk will be greater than 1.33. Anything less than 1 is considered unacceptable. Note: Cg and Cgk are not covered by AIAG's MSA book. Check your regulatory or advisory guidance for acceptability for Cg and Cgk.

Type 1 Cg Math

Type 1 Cg

Understanding Cg¶

Using the defaults for Percent of Tolerance and Number of Standard deviation, the equation for Cg simplifies to the following.

Type Cg Simple

Keep in mind that "sigma study" is the standard deviation of repeated measurements of the same part. Thus, it is an estimate of repeatability. Cg is therefore the ratio of 20% of the tolerance (USL-LSL = Tolerance) divided by 6SigmaStudy. If Cg were equal to one, then 6SigmaStudy would be equal to 20% of the tolerance. As Cg increases, the measurement system is a smaller portion of the total tolerance.

Percent Repeatability¶

Percent repeatability is the ratio of 6*SigmaStudy divided by the tolerance. Note that a Cg = 1 corresponds to a % Repeatability = .2 (assuming default values for Percent of Tolerance and Number of Standard Deviations).

Smaller values of % Repeatability are desirable.

Percent Repeatability

Control chart¶

The individuals chart is used to ensure the measurement process is in control.