Calibration was the act of setting a measuring tool to ensure accuracy.
When the Romulan Admiral Alidar Jarok, who defected to the USS Enterprise-D in 2366, he requested from the ship's replicator a glass of water at the temperature of twelve onkians. The Enterprise computer was not familiar with that unit, and informed Jarok that "[t]his system is calibrated to the Celsius metric system." The clearly irritated Jarok then clarified, "[a]ny temperature at all on the cold side of whatever your system is." (TNG: "The Defector")