The main goal is to provide a calibration for what ever euro coin you have in your pocket.
This is a pretty basic calibration piece, howsoever it is more powerfull then it seems.
By uncommenting one of the avaliable coins on the bottom of this code you can generate a calibration piece which should have the exact measures (height and diameter) for the Euro piece you have avaliable. There's not much to do, simply uncomment your favorite calibration coin, export the stl (Design -> export STL), slice it, print it, put your coin in the center and calibrate.
For reference: the measures were taken from this  German Wikipedia article