Dependence of the peak impact parameter on the ratio ﹩t_{\sigma n}/ t_{\mathrm{FWHM}\,}=\xi _{n}/ w﹩ for several values of n. This ratio varies significantly for β between a few tenths and a hundredth. Thus, it may be feasible to make a crude measurement of β from measurements of ﹩t_{\sigma n}﹩ and ﹩t_{\mathrm{FWHM}\,}﹩.