by the International Bureau of Weights and Measures 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 (of the calibrated instrument or secondary standard)
and, in a second step, uses this information to establish a relation for obtaining a measurement result from an indication.
The concept of traceability of measurement
The International Vocabulary of Basic and General Terms in Metrology (VIM) defines traceability as:
Property of the result of a measurement or the value of a standard whereby it can be related to stated references, usually national or international standards, through an unbroken chain of comparisons all having stated uncertainties.
What does it mean to calibrate an instrument?
In general use, calibration is often regarded as including the process of adjusting the output or indication on a measurement instrument to agree with value of the applied standard, within a specified accuracy.