The Collaborative International Dictionary of English v.0.48:

Calibration \Cal`ibra"*tion\, n.
   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.
   [1913 Webster]

WordNet (r) 3.0 (2006):

calibration
    n 1: the act of checking or adjusting (by comparison with a
         standard) the accuracy of a measuring instrument; "the
         thermometer needed calibration" [syn: calibration,
         standardization, standardisation]