I just engraved a 15cm long line and the real length is 13.8cm.
I read how to fix this but none of the example was for LaserDRW which is (I think) the only program (which I prefer not to change) that works with my machine.
I just realized the problem, it did it only on straight lines and not on squares and turns out that the width of a straight line there is not really clear...
Anyway I don't use lines only simple squares...