I mean how you figure out the length of the stirrup for jumping? I've been in several places (for lessons) and in each they put my legs on different length. So what is the correct way (if any) to choose the appropriate length?
The rule of thumb is, with your foot hanging out of the stirrup, your ankle bone should hit the tread of the stirrup or slightly above. It varies a little depending on how long your legs are. Ideally when you're going over a fence, your leg be at a 110 degree angle, but you just have to play with it a bit. If you feel like you're reaching for the stirrups, shorten an hole and keep trying until you feel secure in your 2 point position.