Radiating a photon from the initial state provides a useful tool for studying a range of low energy physics using a high-energy e⁺ e^- accelerator. Accurate results require careful calculation of the first order virtual photon corrections. We compare exact results for initial state radiative corrections, finding agreement to an order of 10^-5 or better as a fraction of the Born cross-section for most of the range of photon energies, at CMS energies relevant in both high-energy collision and radiative return experiments.

PACS numbers: 12.15.Lk, 13.66.De