Histogram of the residual rotation angle difference between theory and calibrated HiVIS daytime sky polarization spectra. The angular difference between theoretical Rayleigh sky input polarization and the calibrated HiVIS measurements on the Poincaré sphere is computed. There are 19 separate spectral orders spectrally averaged to 50 points per spectral order used to create the Histograms. Calibrations were derived using April 21st 2012 data and applied to observations from April 22nd 2012 giving residual angular error of 1° to 2° between theoretical sky models and calibrated observations. Calibrations were also derived using both April 21 and 22nd 2012 data which were applied to May 10th 2012 observations. In this case, the residual angular error is more typically in the range of 3° to 6°.