Heated bed calibration

I use this tools for RigidBot heated bed calibration.
Precondition:
Use the "Heated bed spring fitting" (http://www.thingiverse.com/thing:515186/#files) to ensure that dimension and distance are equal.
The procedure is than as follows:
1.) Turn off printer
2.) Move up Z-axis manually
3.) Place Z_axis_distance part on left and right side as visible on first picture.
4.) Move down Z-axis until gantry touches Z_axis_distance part
5.) Adjust all four heated bed screws until they are