Hi Dorothy

I basically agree with the opinions stated already.
But it is possible to calculate the range of variation between 2 CMM's by comparing their data sheet specifications:

Let me give an example:
CMM A: Measuring error (E or U3): 2.2 + L / 250
CMM B: Measuring error (E or U3): 3.0 + L / 200

You measure the same feature (for example ring gauge, diam. 200mm) on both machines.
For this feature you can expect the individual machine errors to be within following range:
CMM A: 2.2 + 200/250 = +- 3.0µm
CMM B: 3.0 + 200/200 = +- 4.0µm

Under the assumption that both CMM's are within their specs, but CMM A at the negative limit ( - 3µm ) and CMM B at the positive limit ( + 4µm ), you could expect results to be up to 7µm apart.

For a length measurement of 600mm these 2 CMM's could be already (-4.6 +6.0) 10.6µm apart.

As has been said before, you either have to measure a gage when you want to compare CMM's or you at least you must make sure that exactly the same probing points at the same position are taken.
And the range depends very much on the length resp. diameter.

Best regards

Juergen