Jack,
I do not profess to be an expert but, I have had to perform Gage R&R's on CMM's for 10 years. The main reason my company had been doing these are from requirements from Ford, GM, and Chrysler. With ISO/QS 9000, it is also required to perform studies to prove your machine is capable. It might be accurate when being calibrated, but not be capable based on many factors. If it is not capable, then you can not trust the readings to be correct.

On a CNC/DCC CMM, the operator bias is reduced but could influence part setup reproducibility. If the CMM is a manual machine, operator bias could be a large factor in determining capability. The operator might require re-training to use the machine correctly to be able to reproduce the results.

On the other hand, the operator might be well trained, but the CMM can not repeat the results due to machine error. Some of the machine errors that can be shown include improper calibration, worn or damaged parts, environmental influences, etc.

To get more information on performing Gage R&R's and understanding them, try picking up the 'Measurement Systems Analysis' manual published by AIAG.

You might want to look at performing Gage R&Rs on all of your inspection equipment. The same type of study could show that some of your equipment may have to be replaced or redesigned.