Gage Repeatability assesses the ability of the gage or measurement system to give consistent readings when the same appraiser measures the same part multiple times with the same device. It is a measure of the inherent precision of the gage.
Repeatability is a part of Gage Repeatability and Reproducibility (R&R) studies performed on continuous data, usually in the manufacturing environment. In the mathematical analysis, it is calculated as the Equipment Variation (EV) which is the variation in the measurements obtained by a single appraiser with the same equipment/gage over several trials, with no change in the setup between trials.
A high equipment variation indicates that the gage is not reliable enough for quality control purposes and corrective action needs to be taken to for its improvement, either by repair, redesign or replacement of the gage.
ASQ's Toolbox - Gage Repeatability - http://www.asq.org/learn-about-quality/gage-repeatability/overview/tutorial.html