a method of measurement according to which the difference between a known physical quantity and a physical quantity that is being measured is established. The known quantity is most frequently reproduced by a measure. If the difference between the quantity being measured and the known quantity is small, the measurement error will depend mainly on the accuracy to which the known quantity has been determined. For example, if the difference does not exceed 0.01 of the quantity being measured, its measurement with an error of 0.1 percent will contribute an error not exceeding 0.001 percent to the overall result.
The differential method of measurement is of great importance in checking measuring devices, which is the comparison with a standard of the measure being checked (for example, standard cells connected in counterseries). The differential method is also used in testing materials and articles by means of comparison with a standard sample. The differential method is called the relative method when applied to linear measurements, and it becomes the zero method of measurement if the difference between the known quantity and the quantity being measured is set to zero (to achieve this result, the known quantity must be adjustable).
K. P. SHIROKOV