Bed leveling measurement tool.

For leveling the bed on a (delta) 3D printer, you move the head to different positions near each of the three towers and then adjust a screw to make the head come out at the same height above the bed in each of the corners.

If you place this at the right spot near one of the towers, you can command the head to move to that tower, at say 35mm height, and then to come down to 23.2 (this is the height with the default settings). When all goes well, you hit the middle of the platform on the short end of the see-saw. (make sure the hotend is COLD! :-) ) and the indicator will move up. The middle of the scale is what you're aiming for.

Adjust the "go to" height at the first tower to put the stick in the middle. Then move over to the next tower and adjust the endstop to make the stick end up in the middle here as well. Continue this way on the third tower. Now your bed should be level. If necessary, you can now repeat this in the middle of the bed to see if you've calibrated your rod