NavList:

I must be a real celestial philistine.  I always have to think twice when I read zenith distance, because I can never remember whose zenith.  I use co-altitude instead; that makes sense to me.  Apart from V=IR, S=VT, and p=mf, I’m not much good at remembering formulae these days, so for mer-pass calculations, I end up drawing a fresh 2D diagram every time.  Then you don’t need to worry about when to use plus and when to use minus in a standard formula. Am I the only one? I appreciate it might be different when you’ve not slept for two days, the doghouse smells of diesel, and a waves just gone down the inside of your sea-boot.  DaveP