For the the exams I used to remember it like this:
PET: remember DHOH! (Homer Simpson quote)
Distance x gs Home / (gs Out + gs Home)
and for PSR: THEOH (someones name)
Time to psr = gs Home x safe Endurance/ (gs Out+ gs Home)
others said that (FF-Climb) would be a better definition for safe endurance, but it doesn't have an E in it.
