Accuracy - The degree of an indicated value to an accepted standard value or true value.
Calibration - correcting or determining the error of an existing scale or of evaluating one quantity in terms of reading from another.
Factory calibration - adjust all the internal working of the instrument to bring it into agreement with the standard.
Field calibration - compare one instrument with another instrument.
The other important terms are
Error - Measurement error is the difference between the measured value of a quantity and its true value.
Precision - Precision refers to how close together a series of measurements are to each other.
Accuracy - Accuracy refers to how close a measured value is to an accepted value.