In this method the value of the quantity to be measured is compared with known value of the same quantity or other quantity practically related to it. So, in this method only the deviations from a master gauge are determined, e.g., dial indicators, or other comparators.
It is a method of measurement by direct comparison in which the value of the quantity measured is first balanced by an initial known value A of the same quantity, then the value of the quantity measured is put in place of this known value and is balanced again by another known value B. If the position of the element indicating equilibrium is the same in both cases, the value of the quantity to be measured is root of AB . For example, determination of a mass by means of a balance and known weights, using the Gauss double weighing