Calibration is the process of aligning the measurements from the measuring instrument (gage) with those of an accepted and traceable universal standard. This procedure ensures that the accuracy and precision of the measurements taken by the instrument are within acceptable levels.
Calibration can be used to eliminate bias (error) in the measuring device, if it exists. Gage R&R (Repeatability and Reproducibility) studies do not directly address this issue, although they do identify and quantify bias in the device.
A calibration procedure involves documenting and maintaining records of the steps followed in the calibration procedure, including how often the procedure is conducted and the problems encountered/fixed.
More on Calibration: - http://www.itl.nist.gov/div898/handbook/mpc/section3/mpc3.htm Gage Calibration from Quality Digest: - http://www.qualitydigest.com/feb97/gagecal.html