3D Printer Bed Probing
This is what 4 point bed probing looks like on D3D v19.04 of 3D Printer Genealogy. This should apply to D3D v19.11 and D3D v20.07 because all of these are running the same firmware bed probing settings as File:Marlin D3D Pro v1.0.zip.
The boundary is (40,40) to (120,120).
It turns out that the probing sequence is a C pattern drawn starting at the lower right corner of the C:
(x,y) = (120,40)->(40,40)-> (120,40)-> (120,120).