The relative distance between the bed and the nozzle depends on your Promega configuration (K'tana vs. Compound, glass vs. no glass, etc.) Ideally whenever you home the printer and send the command G1 X0 Y0 Z0 (telling the printer to go to (0,0,0)) the print bed will touch the nozzle. However, as outlined above, the relative distance between the bed and the nozzle varies depending on your setup. Follow the steps below to update the Z configuration of your printer.