Hey all I have finally got my prusa i3 going and printing some good stuff. However everything is 0.8mm to big in the x and y directions for example If I print a 20mm test cube its actually 20.8mm in the x and y directions. How do I go about making my prints dimensionally perfect? I have checked that the x and y axis both move 100mm when commanded to in pronterface so I know they are calibrated correctly.

At the moment I am just adjusting the scale in slic3r to get the dimensions correct but there must be a proper way of doing it?