This plot shows the measured total polarimetry (P = sqrt(Q^2 + U^2)) of the high polarimetric standard star minus the 
tabulated total polarimetry registered for this star: qc_P_offset. Only V-band values are tabulated for the high polarized standard stars.
Trending plots for the R and I band assume that the real (but not tabulated) R and I band polarimetric values are those of the V band.
All values are given in per cent.
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For the non-polarized standard stars the measured total polarimetry is shown (qc_P).