# BiLinear bed leveling

My G29 command reports

``+0.178 +0.281 +0.830 -0.614 -0.012 +0.371 -1.208 -0.849 -0.351 ``

So should I tighten up the screw of the bed, close to 0,0 position or loosen it?

I have a feeling that when I loosen it, it gets away from zero and I expect the opposite to happen.

For bed leveling i use a capacitive probe and after playing around with the screws here is the result

``+0.406 +0.127 +0.411 -0.161 -0.007 -0.041 -0.572 -0.652 -0.668 ``

Finally the leveling process was found here But the question remains. The value `-0.572` corresponds close to `0,0` ?

Proper leveling using plain "A4" or "Letter" paper is recommended. Level the bed by first homing all axes, then level each corner and at mid-span. In between leveling (by dragging the nozzle head from one to another position, beware of the hot nozzle!) redirect the nozzle to "Z=0" or home Z and instruct the printer to go to "Z=0".

Note that capacitive probe sensors are inaccurate, they tend to be influenced by the humidity of air.

Running Marlin Firmware and instructing a `G29` trough a terminal gives me something in the region of the unity matrix:

``Recv: Bed Level Correction Matrix: Recv: +0.999994 +0.000000 -0.003585 Recv: +0.000003 +1.000000 +0.000823 Recv: +0.003585 -0.000823 +0.999993 ``

Running the command `G29 P3 V4` gives:

NOTE:

• `P` Set the size of the grid that will be probed (P x P points)
• `V` Set the verbose level (0-4)
``Recv: G29 Auto Bed Leveling Recv: Bed X: 25.000 Y: 22.000 Z: 0.138 Recv: Bed X: 109.000 Y: 22.000 Z: 0.071 Recv: Bed X: 193.000 Y: 22.000 Z: -0.842 Recv: Bed X: 193.000 Y: 97.000 Z: -0.427 Recv: Bed X: 109.000 Y: 97.000 Z: 0.083 Recv: Bed X: 25.000 Y: 97.000 Z: 0.086 Recv: Bed X: 25.000 Y: 172.000 Z: 0.004 Recv: Bed X: 109.000 Y: 172.000 Z: 0.019 Recv: Bed X: 193.000 Y: 172.000 Z: -0.297 Recv: Eqn coefficients: a: -0.00356075 b: 0.00080090 d: 2.38097906 Recv: Mean of sampled points: 2.07054519 Recv: Recv: Bed Height Topography: Recv: +--- BACK --+ Recv: | | Recv: L | (+) | R Recv: E | | I Recv: F | (-) N (+) | G Recv: T | | H Recv: | (-) | T Recv: | | Recv: O-- FRONT --+ Recv: (0,0) Recv: 0.13385 0.14866 -0.16731 Recv: 0.21531 0.21284 -0.29814 Recv: 0.26715 0.20050 -0.71286 Recv: Recv: Corrected Bed Height vs. Bed Topology: Recv: 0.12837 0.44228 0.42541 Recv: 0.26990 0.56653 0.35465 Recv: 0.38180 0.61425 0.00000 Recv: Recv: Bed Level Correction Matrix: Recv: +0.999994 +0.000000 -0.003561 Recv: +0.000003 +1.000000 +0.000801 Recv: +0.003561 -0.000801 +0.999993 ``

Running the command `G29 P3 V4` again, but now with my vernier on the bed (opposite to the side of the origin, on the right side of the bed; vernier under probing points 3 and 4), gives:

``Recv: G29 Auto Bed Leveling Recv: Bed X: 25.000 Y: 22.000 Z: -0.003 Recv: Bed X: 109.000 Y: 22.000 Z: -0.050 Recv: Bed X: 193.000 Y: 22.000 Z: **5.709** Recv: Bed X: 193.000 Y: 97.000 Z: **5.892** Recv: Bed X: 109.000 Y: 97.000 Z: 0.007 Recv: Bed X: 25.000 Y: 97.000 Z: 0.039 Recv: Bed X: 25.000 Y: 172.000 Z: -0.023 Recv: Bed X: 109.000 Y: 172.000 Z: 0.017 Recv: Bed X: 193.000 Y: 172.000 Z: -0.329 Recv: Eqn coefficients: a: 0.02233918 b: -0.01331358 d: 2.30744504 Recv: Mean of sampled points: 3.45099973 Recv: Recv: Bed Height Topography: Recv: +--- BACK --+ Recv: | | Recv: L | (+) | R Recv: E | | I Recv: F | (-) N (+) | G Recv: T | | H Recv: | (-) | T Recv: | | Recv: O-- FRONT --+ Recv: (0,0) Recv: -1.27376 -1.23426 -1.57986 Recv: -1.21205 -1.24414 4.64083 Recv: -1.25401 -1.30091 4.45816 Recv: Recv: Corrected Bed Height vs. Bed Topology: Recv: 4.05814 2.22162 0.00000 Recv: 3.12192 1.21381 5.22275 Recv: 2.08203 0.15910 4.04215 Recv: Recv: Bed Level Correction Matrix: Recv: +0.999750 +0.000000 +0.022334 Recv: +0.000297 +0.999911 -0.013306 Recv: -0.022332 +0.013309 +0.999662 ``

From the snippets you can see that the topology is printed in the output. You also see the vernier of about 4.5 mm comming back in the matrices. But the 4.5 mm thickness of the vernier is not easily found in the correction matrix!

The answer to your question is that the origin is in the lower left of the matrix, so you need to loosen the origin screw in the first example (this matrix shows you that the bed is highest at the right-back and lowest at the origin at the left-front). Your second example shows that the whole bed is tilted downwards to the front.