It was shown in the course of developing the high-accuracy universal polarimeter (HAUP) that any polarimetric optical analyses cannot be free from a systematic error γ originating in the parasitic ellipticities of the constituent Nicol prisms. A method by which one can remove γ in the HAUP method is presented. This has been successfully applied to measurements of the gyration tensors and birefringence of two enantiomorphic crystals of α-quartz. It was found that the order of magnitude of this error for a polarizer is about 10−4 and consequently γ lies between 10−4 and 10−3 in typical optical systems. Our results, g11 = 5.7 ± 0.52 × 10−5 and g33 = −13.6 ± 0.52 × 10−5 with a wavelength of 6328 Å for laevorotatory quartz at 300 K are in good agreement with some of the previous reports.