goto the menu :CONFIG then :MOTOR TUNING under that.

In the left lower corner of the dialogue box is "steps per".

Your error is not consistent, so there is more to this, it looks like you need to move 5% more which needs 5% more "steps per" in the triangle example the error is closer to 10% presuming it is an equilateral triangle.

The same dialog enables you to set the acceleration, if that is wound up too high then it will cause you problems, so till you have steps per correct I suggest you wind the acceleration right down.

You need to remove backlash from the equation by moving in a direction before stopping and then continuing motion for the purpose of measurement. So dont just move from Y0 to Y100, first move to Y-10, then Y0 then Y100 and measure the Y0 Y100 progress.

Note the settings before you hack them ;-) Someone cleverer than I might be able to tell you exactly what to change it to but suck it and see has always worked for me.

hope that helps you.

Jon