Primary-level calibration of master gears requires quantifying the measurement uncertainty on the artifact being calibrated by a method that does not rely on a transfer comparison. The measurement decomposition method@ developed jointly by National Institute of Standards and Technology (NIST) and Oak Ridge Metrology Center (ORMC) personnel@ is used to determine the uncertainty of each component of the measurement task. Once quantified@ these components are added in quadrature according to NIST Technical Note 1297@ 1994 Edition. Verification of this method can be accomplished by inter-comparisons with other methods and laboratories. The techniques developed at NIST and ORMC utilize a CMM with a rotary table@ a FORTRAN program for involute data generation@ and a ProEngineer solid model for gear visualization.