A bed leveling tool based on the dial indicator (0.4mm clearence) by Turbo_SunShine. I flattened it and put a somewhat longer indicator arm on it for better precision. Fits the Ender 3 and CR-10 carriage. Possibly others as well.

Place the indicator between the carriage and the x-gantry and lock it in place with the lock pin. Then lower the gantry at different locations on the bed and dial in the bed adjustment screws. A simple g-code file can also be made to automate the process. I have uploaded my g-code file for you to modify to fit your printers. More information on how to do the leveling is inside the g-code file.

Important: The indicator goes down lower than the nozzle. Be careful so you don't lower the gantry to much, or you might break the tool. Remember also to remove it from the carriage before you start printing!