Top left: power-law input spectra with a spectral index ranging from −6.0 to −1.5 in steps of 0.1. Bottom left: response function of the seventh histogram channel. Top right: channels response factors, calculated using Eq. (4), plotted against an energy interval around the channel’s nominal energy range. The effective energy E_eff and characteristic response R_BT are indicated by dotted horizontal and vertical lines, respectively. Bottom right: total distance between the response factors (see text), with effective energy corresponding to the minimum of this distance.