A lot of times you hear people using the word calibration and certification interchangeably. Like synonyms. However, these two terms don’t mean the same thing. Calibration refers to the process of repairing or adjusting an instrument so that it functions as it is supposed to function. Certification refers to the process of studying and recording the performance of the instrument to determine if its results fall within its design tolerances. If it does perform within its design tolerances, then the certifying company can issue a certificate in that regard. Take for example a 100 PSI pressure gauge with a +/- 1% accuracy. If the gauge is on the desk top and is reading 20 PSI when it is not part of a system and has no pressure directed to it, then the first step would be to calibrate it. The gauge would be taken apart, examined, repaired or adjusted until it was showing a zero pressure. Once the gauge was calibrated, the gauge could then be tested. If during the test, the gauge was found to be within 1% accuracy, then the gauge could be certified as being a gauge with +/- 1% of accuracy.