Calibration and Adjustment – Clarification of Terms
The International Bureau of Weights and Measures (BIPM) and the Joint Committee for Guides in Metrology (JCGM) have produced a valuable tool to assist with the standardization of weighing terms called the International Vocabulary of Metrology (VIM). In it, item 2.39 defines calibration as an aspect of how a balance operates:
"Operation that, under specified conditions, in a first step, establishes a relation between the quantity values with measurement uncertainties provided by measurement standards and corresponding indications with associated measurement uncertainties and, in a second step, uses this information to establish a relation for obtaining a measurement result from an indication."
In other words, a weighing device is calibrated to understand and document how it behaves. The above definition also clearly states that the derivation of measurement uncertainty is an integral part of calibration. A calibration without a statement of measurement uncertainty is incomplete and becomes a spot check at best.
While the calibration states how a weighing device behaves, adjustment of the device changes its behavior. Adjustment is defined in the VIM as follows:
"Set of operations carried out on a measuring system so that it provides prescribed indications corresponding to given values of a quantity to be measured."
Therefore, adjusting an instrument means modifying its indications in a way that allows them to correspond – as much as possible – to the quantity values of the measurement standards applied.