The accuracy of spectrophotometric measurements is limited by the standards that are used to calibrate the instrument. Therefore, the procedure used in transferring the spectral reflectance factor scale from one material to another for use in calibration must induce the minimum amount of error. The Munsell Color Science Laboratory has been transferring the spectral reflectance factor scale to calibration materials using a statistical method to correct for the most pervasive systematic errors in the measurement process. This method is based on a statistical procedure in which a set of systematic spectrophotometric errors are estimated based on the measurement of seven NIST primary standards and corrected in subsequent measurements. The optimization of the spectral reflectance factor scale to NIST standards minimizes the induced error. The average reflectance factor error consistently found between the corrected measurements of the NIST standards and their certificate values have been 0.0006 and the average Delta E *(ab) has been on the order of 0.2.