Resource Centers
Improving Measurement Systems
The key to improving the measurement system is to get to the root cause of the problem.
- The results of the GR&R study can help here.
- Use the relative magnitude of both the Repeatability and Reproducibility to determine where to start the investigation.
If the Repeatability calculation is greater than the Reproducibility:
- Begin by looking at the measurement equipment since repeatability deals with variation due to the test equipment.
- Here are some possible causes of a high repeatability calculation:
- Measurement device may need to be repaired.
- The device or fixture is not rigid enough for the measurement being made.
- Measurement discrimination cannot meet the level of precision necessary for measuring the part.
- Excessive within-part variation can also appear as a measurement repeatability problem (for example a round part that is not concentric).
- Lighting may make it difficult to accurately read the scale of the instrument.
If the Reproducibility calculation is greater than the Repeatability:
- First look at the appraisers and their test methods.
- Here are some possible causes of a high reproducibility rating:
- Is one appraiser’s overall average part measurement significantly different than the others? Retraining is needed.
- Appraisers may have a hard time reading the gage or device.
- The part or sample could be too difficult to handle or too awkward to align while taking a measurement.