That's very helpful, thanks Mike.
I didn't end up doing that much physics at school, so I'm just trying to work everything out now. I think the setup you are describing sounds pretty good. I've also read somewhere that the actual weight of the scales you use needs to be accounted for, is that right? And using that setup, do the scales display the total draw weight (not half draw weight as some other setups do, possibly incorrectly)?
I like lostarrows velcro strap setup in the original post, seems to make draw length and handle thickness etcetc a bit less confusing. I was also thinking of making the cradle where the bow sits movable so different styles of bow/handle can be taken into account, if i were to make a wooden one.