Clarence N Hickman the Father of Scientific Archery, is the title of a book I've had for many years. He was a prolific inventor of all sorts of things* and designed the first modern recurves.
He built a machine which would draw the graph of draw weight vs draw length automatically.
You stood on a plate to hold the machine down, hooked the bow string onto it and pulled the bow upwards. As you pulled up, a plate with a sheet of paper was pulled across, and as the draw weight increased a pen linked to a spring balance moved up drawing the graph.
I'm trying to build myself such a machine just for the fun of it, rather than the serious research he did it for.
Essentially there are two parts, the horizontal travel where the 28" draw becomes about 12" of movement of a sheet of paper, and the vertical travel where the movement of the spring scale is translated into about 8" of pen travel.
The spring balance is a vital part of the machine, and because I recently bought a new dial balance for measuring draw weight, my old spring balance is now available to be recycled into the machine.
I'll post some pics once the first bit (horizontal travel section) is complete. It will be a bit rough and ready as I'm designing it as I go along and it's mostly wooden construction.
* High speed photography, rocketry, acoustics. He was also an amateur magican.
The book is ISBN 0-9613582-003 for anyone interested.