The mechanism is built with wood, screws and bent wire coathanger, this is so that it can be taken to bits and re-made in a better and more reliable fashion, this is just the mk1, or to use modern engineering parlance a 'proof of concept model'. I prefer the good old fashioned term 'prototype' myself but one has to keep up to date (cough, splutter). Got a bit more done this evening,
It works ok, but the string needs to attached carefully at one side of the roller to get it to track correctly and the plate which will hold the graph paper will need a top guide as it gets kicked off at the slightest provocation.
The wire hook will hook over the bow between your hands as you pull the bow upwards, 28" of travel makes the graph plate slide along about 10".
I've mounted the spring and fitted two lengths of 16mm diameter steel tube to a plate of 1"ply to become the base. Hopefully I'll have some sort of basic working arrangement soon.