In engineering, instrument performance indicators are usually described by accuracy (also known as accuracy), variation, and sensitivity. Instrument workers usually calibrate instruments for accuracy, variation, and sensitivity. Variation refers to the maximum difference between the indicated values of the instrument when the measured variable (which can be understood as an input signal) of the instrument reaches the same value from different directions multiple times, or the extent to which the measured parameter changes from small to large (positive characteristic) and the measured parameter changes from large to small (reverse characteristic) with the external conditions unchanged. The difference between the two is the instrument variation.