A general polarimeter for the precise measurement of Stokes intensities was developed and was used for testing the Sacramento Peak Vacuum Tower Telescope and other optical instrumentation. The design is based upon the polarimeter described by F. Orrall [Solar Magnetic Fields, IAU (1971)] and M. Makita et al. [Ann. Tokyo Astron. Obs. 19 (1982)], with some simplifications. A control computer sets parameters in the integration electronics and provides simple readout for an experiment control or analysis computer. Calibration of the polarimeter is defined by a Mueller matrix for the system; the calibration matrix compensates for the systematics of the polarimeter. The calibration matrix was derived using an optical wheel containing many orientations of sheet polarizers, partial polarizers, and insertable wave plates. The rms of the calibration solution is about 0.6%. The calibration procedure as it is presently defined limits the accuracy of the polarimeter.