1) The process of comparing an instrument's output signal with
reality. Instruments that measure solar energy tend to "
drift", that is, their output signals do not
mean the same thing from one time
period to another. Because of this, they are periodically (annually or semi-annually) re-calibrated against more reliable instruments.
2) Adjusting a measuring instrument to make it accurate. The
set of operations which establish, under specified conditions, the relationship between values indicated by a measuring instrument or measuring system and the corresponding values of a quantity realized by a reference standard.
3) The act of adjusting the color of one device relative to another, such as a monitor to a printer, or a scanner to a film recorder. Or, it
may be the process of adjusting the color of one device to some established standard.