noun (n)

• the act of checking or adjusting (by comparison with a standard) the accuracy of a measuring instrument(noun.act)

  Example:
  The thermometer needed calibration.
  

  Synonym:
  standardisation, standardization
  

  source: wordnet30
• The process of estimating the caliber a tube, as of a thermometer tube, in order to graduate it to a scale of degrees; also, more generally, the determination of the true value of the spaces in any graduated instrument.(noun)

  source: webster1913