A measurement error is the difference between a measured value of quantity and its true value. Such errors tend to become more frequent the longer a device is in operation. At some time, the deviations might be so great that they are no longer within the specifications, which means that quality is no longer assured.

By calibrating the device, the measurement error can be determined and documented. If the measurements are outside the permissible range, the device needs to be adjusted. In this process, the measuring instrument is reconfigured so that measurement errors are minimized and deviations from the set point value are within the device specifications.