I found this much more helpful to calibrate the probe height.
Mesh bed compensation
Checking the trigger height
The Z probe trigger height must not vary significantly with XY position. Measure the trigger height of your Z probe at various XY positions and make sure it is consistent. To measure the trigger height:
Make sure there is no filament stuck to the nozzle (you may want to do this test with the nozzle hot)
Cancel any existing bed compensation by sending M561
Send M208 S1 Z-3 to temporarily allow Z moves down to Z=-3mm. This is to ensure that you can lower the nozzle all the way to the bed in step 5.
Command the print head to the coordinates you want to probe. To probe the center, send G1 Z1.
Command the print head down in small steps until the nozzle just touches the bed or just grips a sheet of paper. You may need to send M564 S0 to allow movement lower than where the firmware thinks Z=0 is. You may also wish to create a macro to lower the head by e.g. 0.02mm to get greater accuracy (G91 followed by G1 Z-0.02).
Send G92 Z0 to define that height as Z=0
Command the nozzle up 5mm (G1 Z5)
Send G30 S-1 to probe the bed without resetting the Z=0 position
Read off the Z height from the web interface. That is the trigger height.
Repeat the previous two steps a couple of times to make sure you are getting a consistent result
Repeat steps 4-10 for the other XY positions you want to check.
On a delta printer, it can be quite hard to achieve a consistent trigger height. Z probes that are mounted on the effector are sensitive to any tilting of the effector, because it affects the relative heights of the Z probe and the nozzle. You can reduce this effect by mounting the probe as close to the nozzle as possible. Probing solutions that use the nozzle itself as the probe are usually not affected by effector tilt, but some types are sensitive to the XY position of the nozzle for other reasons.
Once you are satisfied with your trigger height result (should be between 0 and 1mm, depending on your printer), open your config.g file (this can be found in your DuetWebControl), find the G31 command and enter your trigger height as a negative value in the Z parameter (ex. G31 X0 Y0 Z-.43).
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