pulley ratios on 3 pulley axis

[Jonathan]

Here's the update so far, the config set up as 4.5:1 got me closer. over a distance of 150mm on screen the actual travel was 173.5. I've never set up belts before so what next? play with the ratio or the number of steps per mm? it seems a lot to play with the steps. Im using quality pulleys an belt.

That's odd ... it implies the ratio is actually 3.8905:1
You could just enter that ratio and see ... then check it with a DTI to get a more accurate value. There must be more to it though. Are you confident you have the pitch of the screw correct?