I fit the unwrapped retardation of the LC (expressed in nm) as a function of temperature and voltage.
The peak to peak uncertainty is surely about 20 nm due to our 2.5deg azimuth angle we measured with 0V applied to the LC.
Indeed, the largest peak in the residuals appear at the folding voltages.
The rms of the residual is 2.6nm.
For reference I attach to this entry the retardation fit with and without taking into account the temperature of the LC.
Note that here and in previous entry I used the mean of the 3 data taken at every voltage step.
Taking into account the temperature in the fit reduce the residual rms by a factor 2 and the peak to peak by 50%.