The method given by the AIAG MSA manual
1 has the following strict requirements for data collection:
- There must be a known reference value for each part.
- You must have at least 8 parts with reference values that are approximately equidistant intervals.
- The minimum and maximum values must represent the process range.
- Each part must be measured by the gage m=20 times.
- The smallest part must have a number of acceptance = 0; the largest part must have a number of acceptance = 20; and the remaining must have a number of acceptance greater than or equal to 1 and less than or equal to 19.
If you specify the lower tolerance limit, the part with the lowest reference value must have 0 acceptances and the part with the highest reference must have the maximum number of possible acceptances. For the lower limit, as the reference values increase, the number of acceptances increases. If you specify the upper tolerance limit, the part with the lowest reference value must have the maximum number of possible acceptances and the part with the highest reference value must have 0 acceptances. For the upper limit, as the reference values increase, the number of acceptances decrease.
1 Automotive Industry Action Group (AIAG) (2010).
Measurement Systems Analysis Reference Manual, 4th edition. Chrysler, Ford, General Motors Supplier Quality Requirements Task Force