you have the distance between 2 points in the beginning, and then you create a triangle by pushing the bolt.
your old distance is the base of the triangle, and the slack is the other 2 sides of the triangle, directly dependent on how much you push the screw.
visually the distance seems 100mm. if you push the bolt 10mm, the new length will be 50.99*2, so you increased the length by .99*2=1.98mm
The slack depends also on the length of the chain.
I guess it works better if adjust it once, check to see the slack is good, write down the value for the tool. Next time should be a lot faster.
Versys 2015 Green