I received my second printer and the bed was way off, to make it easier to to level I used this to hang off the gantry and get me “pretty close”, then used normal bed leveling techniques to dial it in. Thought it might be handy for others.

Just hook it over your 20x20 gantry and you're good to go!
 

This could also be used to verify your gantry is level with the bed.