Hi

I have yet to see a rational set of instructions on setting up the probe on a bed leveling system. It is one of the most discussed and least understood parts of these systems. Compounding the problem is the fact that signs (which way is +) can change depending on what the reference is.

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A gcode file is generated from an stl by a silcer. The slicer program does a whole bunch of things. One of the many things is to center the stl model up on the print surface. You can tell your silcer how far above or below the surface you want the print to start. Many people find that re-compiling firmware each time you do a different print is a bit of a pain. Changing the Z offset (start of the print) in the slicer can be an easier way to do things. You have to do it one way or the other (firmware or slicer). It's an iterative process that has to be done on each printer after it's built.

In the case of a slicer based adjustment, it can be either negative or positive. The sign simply depends on which direction the offset is being applied in. The standard Marlin firmware has a minimum Z of zero. If you apply an offset of -0.1 mm in your slicer and have a firmware minimum of zero, the offset will be ignored. That makes the process very frustrating ....

Bob