[spaghetti]

the lenght of a circular band is taken between the two edges were the wishbone is attached.
But if you ask WHO and WHY determined that, this is the answer: the length of bands sold with guns of each length are standards derived form testing and experience: worldwide, manufacturers found out that on 75 eurogun a 42cm band gives the best performance, that on a 90cm gun a 48cm band shoots better than any other length option, et cetera et cetera.
Now my question is, and forgive me for asking, but: how much experience do you have with spearguns? I don't mean bulding them, but using them?