Abstract: In the paper, a mathematical expression for errors in measuring effective values of AC voltage and current, and power with multiple averaging under qu asisynchronization is presented and proven. Errors after multiple averaging over the sampled data can be obtained. The number of averages can be determined to give a required accuracy. In addition, relationship between the first sampling p oint and the error is analyzed, and the choice of an optimal starting point for sampling is discussed.

Key words: error, first sampling point
, multiple average, quasi-synchronization