How to determine the error of the electricity meter
The accuracy of the measuring devices is determined by the so-called accuracy class... The most common apartment counters have an accuracy class of 2.5. This means that a perfectly functioning meter can represent 2.5% more or less than its rated power.
An example. The ideal meter for 220 V, 5 A should be considered for 1 hour: 220 x 5 = 1100 Wh. But, taking into account the accuracy class, the meter should be considered operational, taking into account under the same conditions: 1100 + (1100 x 2.5): 100 = 1127.5 Wh, and 1100 — (1100x 2 .5): 100 = 1072.5 Wh
A good meter should operate within the accuracy class at allowable overloads. At a low load, the accuracy of the readings decreases, and at a very low load, the disk of a working counter may not rotate.