Set of operation that establish, under specified condition the relation between
values of quantities indicated by measuring instrument or values represented
by a material measure or reference material and the corresponding valve
realized by standard.

Calibration Set of operations that establish, under specified condition, the
relation between values of quantities indicated by a measuring instrument
or values represented by a material measure or reference material, and
the corresponding value realized by standards.

The device with the known or assigned correctness is called the standard.
The second device is the unit under calibration (UUC), test instrument (TI),
or any of several other names for the device being calibrated.