100% of the time, test equipment contributes some error. Usually the magnitude is small and the cause is unassignable - if you maintain the equipment. Whether your tests are destructive (to the sample) or not, you should be doing weekly or even daily Verification testing (of the same batch of whatever) and Control Charting the results. You should be doing MSA (Measurement Systems Analysis) and probably Uncertainty Budgets. Does your lab have ISO-17025 Accreditation? I hope so. But even if you do all the above, you will still be asked to retest. A test error is the best thing! If it's test error, then maybe there is no problem with materials, process, and sampling that produced the sample you are testing. No need to reject and/or rework - just correct the test! But if you get your test equipment under control, that mindset in the people above you will make sarcasm your constant companion.
