Calibration is the process of ensuring the integrity accuracy of measuring instruments that is the accuracy of a measuring instrument compares with an appropriately calibrated laboratory reference standard. The process of calibration not just ensures the traceability of measurement results to national standards but also the measurements of uncertainties have to identify for the measurements are made.

Digital caliper and extemal micrometer are one-dimensional measuring device and commonly used in the industrial. The calibration characteristics for these small tools are the linear traveling, flatness and parallelism of the measuring faces. The main factors for making quality of measurement results by using these instruments is shall comply with Abbe's law. When we rely on results of measurement, these factors must be established before making any measurement.