(RMS error) 1. the square root of the average of the squared differences of values from their mean 2. GIS the square root of the mean error between the "known" and digitized coordinate locations—note 1. RMS error is calculated when tics are used to register a map on the digitizer; the lower the RMS error, the more accurate the digitizing or transformation —synonym tic registration error —note 2. for highly accurate geographic data, the RMS error should be kept under 0.004 in (0.01 cm); for less accurate data, the value may be higher —see accuracy, ticThis definition last updated 08/17/2008