Dual Extruder Head Calibration improved

This is a slight improvement on
http://www.thingiverse.com/thing:533814
where I have cut off the left lower corner at an angle so you figure out the part orientation after removing from the build plate.

You MUST either measure your errors with the print still on the buildplate OR print with a raft and remove with the print still adhered to the raft (my preferred method). Using this I can get alignment within 50 um on repeated prints.

Advice: 1) print at high resolution and scale up th