The design you linked is a 3D printed part that can be used to move the Z endstop on the UMO+ printer from the top to the bottom. This allows the printer to be calibrated in the same way as the Ultimaker 2, which has a Z endstop at the bottom of the printer. <a href="https://www.zibtek.com/technology">Zibtek</a> notes the design also includes instructions on how to make the necessary firmware modifications to enable software Z leveling.