In measurement technology and metrology, calibration is the comparison of measurement values delivered by a device under test with those of a calibration standard of known accuracy. Such a standard could be another measurement device of known accuracy, a device generating the quantity to be measured such as a voltage, a sound tone, or a physical artifact, such as a meter ruler.

The outcome of the comparison can result in one of the following:

• no significant error being noted on the device under test
• a significant error being noted but no adjustment made
• an adjustment made to correct the error to an acceptable level

Strictly speaking, the term "calibration" means just the act of comparison and does not include any subsequent adjustment.

The calibration standard is normally traceable to a national or international standard held by a metrology body.