This is simply a graphics driver feature that we directly expose. We don’t make up the units, or the meaning of the number; this can actually vary from vendor to vendor. We can’t change the unit because graphics APIs don’t have a feature for doing so.
There is a more reliable alternative to a depth offset, which is to tweak the min/max range that depth values are mapped to when written to the depth buffer. You can slightly bias this range so that values will always be written with an offset. The value here is 0-1 in depth buffer values (note that depth buffers aren’t linear), which is more predictable across graphics cards.
node.setAttrib(DepthOffsetAttrib.make(0, 0.0, 1.0))