Bed Level Correction process

(2021) Thingiverse seems to have destroyed / lost multiple additional stages of instructions and reference photos. I'm not sure it is worth recreating given the advances in automatic mesh bed leveling.

Work-in-progress... would be delighted to incorporate suggestions for improvement. Please comment or message me.
* 2019-09-11 @wabbitguy suggested connecting the patches to make it easier to keep straight which is which while measuring. Was such a great idea, I had the .scad file updated alm