Results from a new technique for the absolute calibration of flats are presented. This technique is mathematically exact and, in addition, computationally nonintensive compared to previous techniques. Hence it allows the calibration of flats to a high degree of precision over the entire surface. The accuracy of this new technique is demonstrated through simulated test cases. This technique is currently implemented in the manufacturing cycle of optics (RMS precision of approximately λ/250 at a wavelength of .6328 microns).