I was recently looking at the setup routines for the BCN3d sigma. Remember that printer is running marlin 1.1 like us, perhaps a bit more customised. There are a number of clever-looking things going on in this video: Quite easy to miss at the very beginning that: a) it uses a simple microswitch endstop next to each nozzle. That endstop never has to be lowered because it only probes the bed in positions where the nozzle is off the edge fo the glass. Since each nozzle manages to probe 3 positions like that, each time that is enough to define a plane. b) the odd thing about this printer is that the two nozzles are on separate heads. Each extruder probes 3 points and two of those points are in common: the ones at the front of the bed. That enables the computer to determine any differences in height that might exist between the nozzles. c) notice that having a perfectly rigid steel bed, and a very stiff linear rail system, I don't think there's any need for meshing. Is there anything we can learn from? Or be inspired by?