Calibration is the procedure of comparing a reference with a known error margin against a device (for example a pressure gauge) under test. If the device doesn’t match the reference, then we adjust it to match, or at least come close, the desired measuring accuracy. The reference measurement instrument must be more accurate than the pressure gauge to be calibrated, and it must also be traceable. To calibrate a pressure gauge, we will need to check the values throughout the entire measuring range, zero point, intermediate values, and the full-scale value.