I'm just curious what others have seen with regards to what the IR sensor is actually measuring. I know there was some talk about it reflecting off the heated bed, not the top of the glass, feels like somewhere in between. Doing some experiments with mbl I was putting a block under the ir to keep nozzles way off the bed. Doing this, I noticed that Z0 was not touching my block, as it would with the regular bed. I also tried with some opaque paper. In the end, opaque materials and seeming color/reflectivity matters as well, most were detecting 1.5-2mm before the glass normally does. Glossy opaque can be even further. I also tried a piece of smoked glass I had, 0.6mm further. Given the glass is about 3.7mm. Seems inconclusive. So just curious if anyone else looked. In the end I'm trying to think how precise this can be for automatic leveling... Also been wondering why we don't just borrow from the cnc world and use electrical contact of the nozzle to a control block of known thickness for true precision.