Mark,

The manufacturer will say in their specs how they certified the machine and what criteria they used. At a minimum they should meet there own specs. I know of one large CMM where it took months to get it to meet the manufacturers specs and another where they never did.

Get a copy of the ASME B89 Standard read it thoroughly and make sure that you understand the difference between repeatability, linear accuracy and volumetric accuracy. Read Bruno Struck's contributions on this forum about the ISO criteria.

I would also suggest that when the service technician is certifying the machine you look at the code and go over it line by line. Be on the look out for coordinate translations that you don't understand.

Look at the compensation tables. If you see columns of zero's after the laser shots have been taken, be suspicious.

Use the largest ball bar or renishaw checking gage arm that will fit in your machine.

Bob Connors
Lawrence Berkeley National Lab