Occasionally it happens to me that I do something wrong here, e.g. normally I would set Material Top to +0.2 and Material Bottom to -3.0.
By accident I entered +3.0. But that does not make sense. When would you start milling at the bottom and move slowly up? I'd like to get an error message whenever the material bottom is higher than the material top.
Currently a tool path is created, touching the material top. Just yesterday I wanted to drill 100 holes and noticed later that I touched 100 times the material but no holes created because of my mistake that went unnoticed.
What would help here as well is a graphical indication of some sort. I remember the first time using that, I said material top = 0 and material bottom = 3 expecting that to be 3mm below. Only later I recognized my error that the bottom is -3mm.