The term calibration is often misused.
Calibration means the comparison of a unit under test (in our case an energy meter or reference standard) with test equipment with higher accuracy. It is a strict comparison to evaluate the accuracy error.
Adjustment involves a manipulation of the unit under test. Electromechanical meters have adjustment screws, electronic meters have special memory for correction values.
After production a energy meter is adjusted first. The target is to bring the meter as close to zero error as possible. Once the meter is adjusted, the performance must be verified.
This is done with a calibration.
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Editor's note: This article was originally published in July 2019 and has been updated for comprehensiveness.