I'm running a G90c 10-10-8 with a renishaw ph10m probe. For no known reason my machine becomes "inaccurate". I know this by running a "test" pc calibrated to specific dimensions. I do use 4 separate indexes on this "test" pc. The results are usually .02 to .05 microns out from calibrated specs on my "test" pc. The only way I have been able to correct problem is by running my requal program. After that all is fine. I run a "test" pc about every 8 hours. Things will be fine and great for days and then again it won't hold for 24hrs. I have changed my ph10m twice and have had no luck. Any Ideas????