Calibration of extruders of reprap Mendel tricolor

The position of the three extruders have to be checked now and then as position can change trough use and while adjusting height (tilting of extruder)
With the calibration plate one can measure if position stored in printer (can be seen with sending command M503 to printer) is OK or has to be changed. In Picture you can see that the blue square is to much to the right. So X position of third extruder has to be adjusted for -2 mm. You can set the correct offsets using G10 P2 X-33.7 Y3.2 Z0 (example)