Execution is from the console and a “SCREWS_TILT_CALCULATE” button will appear as part of the Tool pane of Fluidd's main dashboard as well once the [SCREWS_TILT_ADJUST]] stanza is defined in printer.cfg configuring the bed screw points.

You must first HOME the printer.

$ G28
$ SCREWS_TILT_CALCULATE
// probe at 55.000,180.000 is z=1.365250
// probe at 55.000,180.000 is z=1.365250
// probe at 225.000,180.000 is z=1.377750
// probe at 225.000,180.000 is z=1.381500
// probe at 225.000,10.000 is z=1.375250
// probe at 225.000,10.000 is z=1.376500
// probe at 55.000,10.000 is z=1.391500
// probe at 55.000,10.000 is z=1.392750
// 01:20 means 1 full turn and 20 minutes, CW=clockwise, CCW=counter-clockwise
// rear left screw (base) : x=55.0, y=180.0, z=1.36525
// rear right screw : x=225.0, y=180.0, z=1.37962 : adjust CCW 00:01
// front right screw : x=225.0, y=10.0, z=1.37587 : adjust CCW 00:01
// front left screw : x=55.0, y=10.0, z=1.39212 : adjust CCW 00:02

Here we see SCREWS_TILT_CALCULATE has measured the bed height at the four bed screw positions of the Neptune 4. The rear left bed screw is defined as the first position and at each other bed screw position the height is measured and then used to calculate how much and which direction the other three bed screws need adjusted for the bed height at those positions to match.

Adjust each bed screw as indicated and re-run SCREWS_TILT_CALCULATE until each bed screw is no more than 1 minute from being level, no more than 4 minutes total across all screws.

 
$ SCREWS_TILT_CALCULATE
// probe at 55.000,180.000 is z=1.454000
// probe at 55.000,180.000 is z=1.452750
// probe at 225.000,180.000 is z=1.456500
// probe at 225.000,180.000 is z=1.457750
// probe at 225.000,10.000 is z=1.452750
// probe at 225.000,10.000 is z=1.454000
// probe at 55.000,10.000 is z=1.457750
// probe at 55.000,10.000 is z=1.460250
// 01:20 means 1 full turn and 20 minutes, CW=clockwise, CCW=counter-clockwise
// rear left screw (base) : x=55.0, y=180.0, z=1.45337
// rear right screw : x=225.0, y=180.0, z=1.45712 : adjust CCW 00:00
// front right screw : x=225.0, y=10.0, z=1.45337 : adjust CW 00:00
// front left screw : x=55.0, y=10.0, z=1.45900 : adjust CCW 00:00

The bed is now perfectly level.