I thought I'd share a formula I have used that matches my own preferences pretty perfectly for a "one size fits all" scope zoom scaling, (an updated "uniform soldier aiming" if you will, for games that use many scope zoom levels). As many of you agree focal length or "0% monitor match" is the mathematically principled way to scale, with arbitrary monitor distances effectively being just a hack to mitigate the natural slowdown effect that zooming-in creates when using focal length scaling.