(a) Fractional residuals between the total intensities in a Stokes polarimeter with and without HWP precession. We fix the ratio I_⊥/I_s = 0.502 and consider different HWP precession angles θ₀ = [1°,0.5°,0.25°], normalizing the difference with respect to the maximum intensity of an ideal Stokes polarimeter. (b) Fractional residuals, as before, but in a shorter time interval to highlight the beats induced by precession. (c) Power spectra with peaks at multiples and submultiples of the HWP spinning frequency with an amplitude related to θ₀.