Many of the most important components of the XSTAR calculation require numerical quadratures over energy, and these are generally carried out using straight-forward trapezoid quadratures over a fixed grid of energies. In addition, the computation is speeded by the use of a strictly logarithmic grid spacing in energy. We use 9999 energies spaced logarithmically from 0.1 eV to 20keV. This results in a 0.12 grid spacing, corresponding to, e.g. 8.6 eV at 7 keV. This is the energy resolution of the code.