multi axis delta printer diagonal calibration

Needed an easy print to dial in diagonals measures (A,B,C) for my delta printer. Designed this that is useful to check simmetries and deal with distortion.
1.Orient it so the sides are aligned with the towers
2.Print it
3.label with a pen marker the towers (A,B,C) orientation
4.measure sizes that should be equals. If yes you are fine
5.if not, change the diagonals errors in the firmware (or eeprom) using some proportion....
6.goto 2