Auto Bed leveling algorithm

Hello All,

Can someone explain the logic behind the bed leveling process. I went through the vector_3 cpp and .h files but could not really figure out.
Here is what I get on the comm log

Bed x: 20.00 y: -40.00 z: 0.15
Bed x: 260.00 y: -40.00 z: 0.76
Bed x: 260.00 y: 80.00 z: 1.00
Bed x: 20.00 y: 80.00 z: 0.67
Eqn coefficients: a: 0.00 b: 0.00 d: 0.30
planeNormal x: -0.00 y: -0.00 z: 1.00

Can someone explain how 0.3 was calculated ?