Leverage RichRap's Quick Fit X Carriage to add a precision bed-leveling aid.

Using a dial indicator takes the guesswork out of how level your bed is and since you can just swap it in and out in a flash it's easier to switch right from leveling to printing.

Strictly speaking, this isn't a derivative and instead the .scad script was written from scratch, but it's useless without the carriage so I'm gonna call it a derivative work anyway.