M565 should be negative. As it indicates the nozzle position when the probe senses the bed. The logic here is this: A typical autolevel system works with a retractable probe. The probe extends past the nozzle to sense the bed position. When the probe touches the bed the nozzle is in the air, say 1mm. In this situation M565 would have a value of Z1.0 With the RoBo3D printer, and other printers that uses the nozzle as the probe point, the nozzle touches the bed and the switches activate after this. When the "probe" is activated the nozzle is "in" the bed, thus it's a negative 1mm "into" the bed. In this situation the M565 would have a value of Z-1.0 Any other other option (Slicer, G1, etc) would use a Positive value, as it is raising the nozzle up in the air (out of the bed) to be offset correctly.