Comparing calculated ﹩L_{\mathrm{X}\,}﹩‐values in different cosmologies. Plotted are the changes as a function of redshift, compared to the current ﹩\Omega _{m}=0.3﹩, ﹩\Omega _{\Lambda }=0.7﹩, ﹩H_{0}=70﹩ km s⁻¹ Mpc⁻¹ cosmology. Dotted lines are slight variations on the two basic parameters, without changing the Hubble constant. The solid line is the now obsolete ﹩\Omega _{m}=1﹩, ﹩\Omega _{\Lambda }=0﹩, ﹩H_{0}=50﹩ km s⁻¹ Mpc⁻¹ cosmology. The result of an approximate formula (Pen 1999) for ﹩\Omega _{m}=0.3﹩, ﹩\Omega _{\Lambda }=0.7﹩, ﹩H_{0}=70﹩ km s⁻¹ Mpc⁻¹ is also shown (dashed line).