Summary I don't like idea of calibrating leveling every time before printing. Glass bed is usually very stable after one calibration Auto correction takes controllers CPU time to correct Z values and decrease printing quality and speed. My idea is to make perfect calibration once, with glass bed, fix it, and check its leveling after some time. This module allows you to make level calibration as perfect as possible by using Bed height map option of Repetier-host. Mount micro switch, without leaver, to this module and attach module to the hotend when you want to make calibration. Connect switch to Zmin connection and modify firmware to enable Z probe. I am using Repetier-firmware with RAMPS1.4 and Z probe is on pin 18. Manual calibration can be achieved by modifying Tower X,Y,Z endstop offsets values in EPROM. Just play little bit with values, and after every change re-test Bed height map. If you getting lower difference between lowest and highest value, you are on right path. You do not need to change all tree offsets, just two of them. Once you get difference about 0.1-0.2 between lowest and top values, consider leveling done. Finally, I always confirm my level calibration with large test like this. http://www.thingiverse.com/thing:702690 WARNING: Do NOT power hotend while module is still attached. Module is optimized for E3Dv6 hotend. It is 6mm below hotend nozzle. For those who like Auto configuration, check my YT video and visit forum topic about OpenDACT, http://forum.seemecnc.com/viewtopic.php?f=36&t=8698 https://www.youtube.com/watch?v=8Xt3Te73Xdo https://www.youtube.com/watch?v=cQ1uTnZpUzM