Why is EV divided by n*r in AV calculation?


Starting to get Involved
Hello, I have a question with regards to the following formula in MSA 4th edition:
Why is EV divided by n*r in AV calculation?

Suppose I'm trying to perform regular MSA type 2: 3 operators, 3 repetitions, 10 parts.

I'm trying to calculate Appraiser Variation. As MSA says "Since the appraiser variation is contaminated by the equipment variation, it must be adjusted by subtracting a fraction of the equipment variation"

There are two things I don't understand about this formula:
1) Why don't I subtract the EV? Instead, I have to divide it. From what I understand, the goal should be to exclude the variability that results from EV to get "clear" AV.
2) EV is calculated by taking the average range for 3 operators, so in total it takes ranges from 90 measurements. Why should I divide by 30 and not by 90?
Top Bottom