Pixel-by-pixel comparison of VSM and HMI longitudinal magnetograms observed on 14 November 2011. The HMI magnetogram was spatially smoothed to match VSM resolution. Three panels show scatter plots for various flux ranges (color scale for scatter plots is logarithmic). Shown in solid line is computed fit and in dotted line scaling factor equal unity and zero offset fit. Computed fit (scaling factor and offset, fit standard deviation in parentheses) and Pearson correlation coefficient are given in upper left corner of each panel. Reproduced from Pietarila et al. (2013).