Marlin level corners use probe. Each bit of filament it extrudes needs to stick to something - either the bed (your first level) or to the previous layer of filament you printed. Therefore for 50mm insets the nozzle positions should be; (50, 95), (250, 95), (250, 5), (50, 5). I enabled LEVEL_BED_CORNERS & LEVEL_CORNERS_USE_PROBE , which basically probes a reference corner and then probers each of the other corners. During homing and bed_leveling, the probe is activated automatically. Marlin allows you to take these bed measurements using nothing but a piece of paper, but for an improved experience the best option is to install a bed probe (also called a “Z probe”). My method of using UBL with manually probing has the corners set to 0. Note that this guide only explains how to set up UBL on cartesian printers (motion systems such as CoreXY are included in the definition of “cartesian”). h #define LEVEL_CORNERS_INSET_LFRB { 30, 30, 30, 30 } // (mm) Left, Front, Right, Back insets first number is your x location from zero for your left bed screws. Maybe it is useful to people who can't switch to a Marlin version supporting this. When I activate LEVEL_BED_CORNERS, I have to manually activate the TOUCH_MI probe. f5z48 3rjm 3vxkpm ugk dorugr diui xyzt ldw6cu3 gf3n w27