Gengis
Yeah, I used to do energy calculations in stone-barlycorns just to wind the physics professor up. However I stop at using kgf, let alone mixing systems. There's a perfectly servicable unit called the newton. If you only ever do one sort of calculation I s'pose you can use any units you want that are dimensionally correct. If you do a lot of calculation, best to stay within 1 system. I don't much care which one, I am equally uncomfortable with SI, BES and the various colours and flavours of imperial. Little problems with measurement systems can cause incorrect separation between spacecraft and planets, aircraft and Winnipeg etc.