# Optical Comparator measuring of Position of a Threaded Hole

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#### tonya07

I would be interested in getting your advice on how to explain to our customer the proper way to measure the position of the threaded hole on the Optical Comparator. We currently use the Go end of the threaded plug gage. Zero on the gage, move to the top of the part and take dimension, move to the bottom of the part and take dimension. Find the difference in both dimensions and divide by 2. I understand that if you do not divide by 2 you get the total deviation across the diameter but we really want to know the deviation (offset) from center on the radius.
Is this correct?? If so, can you help me better explain to my customer why we divide by 2? They are not understanding our reasoning.
Our customer only finds the difference between both dimensions (they do not divide by 2).

#### Michael_M

Trusted Information Resource
Re: Optical Comparator measuring of Position

If you are looking for true position the formula is actually:

(A squared) + (B squared) = (C squared) as an example:

deviation of "X" dimension is .0025 and after squaring it you get .00000625

Deviation of "Y" dimension is .0012 and after squaring it you get .00000144

Adding the two dimensions together you get .00000769 which you then take the square root of and get .002773085.

This number is doubled as the calculation gives you radius and we need diameter. So the final true position is .00554617.

The optical competitor can give you the deviation of X and Y which you look like you got.

[Added in Edit] If you are only looking for a single direction check, you do not divide by 2 as you are looking for the diameter of the deviation, not the radius. The description you are showing would be correct without the dividing by 2.

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