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3. Video Link - What is Measurement System Analysis?

4. What is Measurement System Analysis?

5. Q: What is Measurement System Analysis (MSA)?
A: It’s a set of techniques that allow us to answer the question:
IF I USE THIS GAGE TO MEASURE,
HOW MUCH CAN I TRUST THE MEASUREMENTS I GET?
MSA is based on Measurement Error

6. Understanding Measurement Error
Take a single item, and measure it multiple times using the same gage/same technique/same appraiser

7. Understanding Measurement Error
Record the measurements and draw a histogram

8. Understanding Measurement Error
The histogram represents a sample from a normal distribution with a Mean, and a Standard Deviation (derived from spread)

9. Understanding Measurement Error
Consider the position of the mean – This is how we determine the bias of the system
Imagine we had measured a reference size – a standard – of a known dimension.
We could compare the mean of our results to the actual size of the standard.
The difference is Bias

10. Bias
Reference Value = – This is a known size
Mean of multiple measurements = 0.525
The gage is, on average, measuring about too big.
It has a positive bias of 0.025

11. Bias
The gage is, on average, measuring about too small.
It has a negative bias of 0.025

12. Bias
The gage is, on average, measuring the same size as the standard.
It has a zero bias

13. Bias
But, we have only dealt with Bias at one size at one point in time
A Gage is used over a range of sizes
And over a period of time
Bias may change depending on these factors:
Linearity
Change in Bias over the operating range of the gage
Stability
Change in Bias over time

14. Bias
Linearity – Change in Bias over operating range

15. Bias
Stability – Change in Bias over time

16. Bias
Stability & Linearity
For standard Gages - How does the calibration system deal with Bias?

17. Variation
Repeatability & Reproducibility
Bias is based on the location of the mean of the distribution
What about the spread of sizes?
For a perfect gage this spread would be as small as possible
We need to determine if we can live with the spread (variation) of measurement error from the gage
We know that when one person uses the gage we get variation – This is the variation inherent in the Gage – REPEATABILITY
If we have more than one person using the gage, this may introduce more variation - REPRODUCIBILITY

18. Variation
Repeatability & Reproducibility

19. Variation
Gage R&R
One way to determine the amount of variation in the Measurement System is through a Gage R&R Study
Take say, 10 parts, 3 appraisers, and measure each part 3 times ( or 15 parts x 4 appraisers x 5 replicates – whatever you want)
Analyze the results using statistical methods e.g. Analysis of Variance (ANOVA) to determine how much variation comes from
Gage R&R
Repeatability
Reproducibility

20. Variation
Gage R&R
Screenshot from Free Online Gage R&R ANOVA Calculator at

21. Variation
Gage R&R

22. Variation
Gage R&R
When we’ve calculated the magnitude of the
Repeatability
Reproducibility
Both together – Gage R&R
We can compare them to:
A Tolerance
A Process Capability
The amount of Total variation in the Gage R&R Study
Anything else that helps answer the question:
How much can I trust my data if I use this Gage ?

24. Visit:
For more info about:
Measurement System Analysis
Gage R&R
Free Online Gage R&R Calculator (ANOVA)
Interactive Process and Gage Simulation
Other helpful stuff