Assuring the quality of a measurement is crucial. In order to achieve the finest measurement and thereby the correct decision based upon it, calibration of equipment both before and after use is essential. This both establishes (metrological) traceability for the measurement and fulfills the requirements of ISO 9000.
Fundamentally, measurement is a process which checks whether something is correct within a set of specified limits. A decision on the results is based on whether the device being measured is inside or outside those limits. Clearly equipment to carry out the measurement is essential: either a simple gage, scale or thermometer; a more advanced measuring system such as a coordinate measuring machine (CMM); laser or vision based measuring systems; or electrical instruments like power supplies, multimeters, oscilloscopes, signal generators or spectrum/signal analyzers. For every one of these, pre and post measurement calibration is essential to ensure the most accurate outcomes.