The tolerance on all values is 15%. Obviously as the resistance gets lower that tolerance gets smaller and its harder to get an accurate reading. Most everything we'll be coming across is between 5k-50k. As far as calibration, this can be manually verified by using an ohm meter before testing the other pots. The reason I'm pursuing this is because we occasionally get large batches of pots we need to test and this would speed up our process quite a bit.