Signal-to-noise ratio according to Eq. (22) with ℓ_max = 500. F_lim = 10^-13 erg/s/cm² along with 500 counts at this flux is assumed. The upper and lower panels correspond to Models I and II, respectively. In the left-hand panels we show S/N as a function of ΔE and E_shift while keeping E fixed to 3.0 keV. The right-hand panels display S/N as a function of E and ΔE by keeping E_shift equal to ΔE. The dashed S/N contours correspond to values 1, 2, 4, 8, 16, and 32.