Measurement error

[[Ma...]]

I was trying to measure a ring gage to correlate with our ULM system when I noticed that the dimensions were way different.

Ring gage should have measured 2.99996 and CMM is measuring it at 3.00046 a difference of .0005.   Have also checked gage blocks and getting error within .0005 - .00076.

Machine is a Zeiss Prismo with a Vast Gold head.  I have verified that the correct head is selected, the calibration sphere dimensions are accurate, requalified Master, and probe used for inspection has been calibrated as well.

What am I missing?   Is there something else that could be causing this error?

[[Ro...]]

For said ring gage, are you checking it as a max inscribed circle, or LSQ? Do you have filtering and outliers turned on? Temperature can also influence results, so might need to use temp comp as well. 

[[DW...]]

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You are using the R value from the Zeiss certificate right? That's quite the error at 0.0005". Please list measurement strategy and evaluation settings, although with an error that high I would think there is physical damage to your equipment. Whats the probe sigma like?