Here are the possible settings:
BED_LEVELING_METHOD 0
This method measures at the 3 probe points and creates a plane through these points. If you have
a really planar bed this gives the optimum result. The 3 points must not be in one line and have
a long distance to increase numerical stability.
BED_LEVELING_METHOD 1
This measures a grid. Probe point 1 is the origin and points 2 and 3 span a grid. We measure
BED_LEVELING_GRID_SIZE points in each direction and compute a regression plane through all
points. This gives a good overall plane if you have small bumps measuring inaccuracies.
BED_LEVELING_METHOD 2
Bending correcting 4 point measurement. This is for cantilevered beds that have the rotation axis
not at the side but inside the bed. Here we can assume no bending on the axis and a symmetric
bending to both sides of the axis. So probe points 2 and 3 build the symmetric axis and
point 1 is mirrored to 1m across the axis. Using the symmetry we then remove the bending
from 1 and use that as plane.