Dual Extrusion Calibration, just four small cubes (2x2)

in order to have a proper x/y calibration between the two extruders, i designed this simple calibration test:

1) just print it the first time! --> see my try no.1
2) messure the two x-values (1st+2nd cube & 3rd+4th cube) --> 20,8mm and 19,5mm
3) substract them, divide the number by 2 (your two extruders) --> 20,8-19,5 = 1,3 /2 = 0,6mm
4) modify the x-offset in your slicer --> Extruder#1 gets -0,6mm and Extruder#2 gets +0,6mm
5) repeat for the y-values
6) repeat testing until you are happ