α factors from Table 3 plotted versus the acf with energy E > 90 keV for all channels. The different satellites are plotted in different symbols, given in the legend. 0° and 90° detectors are distinguished by open black and solid red symbols, respectively. The NOAA-18 0° detector factors are removed from P4 and P5 in the regression. The best fit line found by regression is plotted in black, with accompanying 95% prediction intervals in dashed blue lines. The standard deviations of α are plotted as vertical lines.