9/1/2020: I've increased the speed and created two versions. A version that uses M0 GCode pause for 8-Bit Ender 3 (V1.x.x board) and an M25 GCode pause version for 32 Bit machines (Ender V2 and Ender 3, Ender 3 Pro with 4.2.x board).
These are in the V4.0  .zip file.
8/13/2020:
I've reduced the filenames to less than 22 characters so they can be used with Creality 32 bit board printers such as Ender 3 V2 with the latest Marlin firmware.
(If you have an Ender 3 V2 running Creality Firmware version 1.01 or 1.02 then use this version https://www.thingiverse.com/thing:4559687/files)
The test print will now print from outside to inside rather than inside to outside.
There are two files required. First run the CHEP_bed_level.gcode file on your Ender 3 or any similar size printer. Adjust each corner by running a piece of paper or Filament Friday sticker under the nozzle until you can barely move it.
Then run the CHEP_bed_level_print.gcode file and live adjust or "adjust on the fly" the bed level knobs to get as close…