I got roughly these values: PLA at 230C: offset -4.8 PC at 285C: offset -4.55 Why does it change so much? Let's say the aluminum heatbreak is 30mm long and 55C hotter... it should expand by 2.4e-5 * 55 * 30 ~= 0.04mm, not 0.25mm. Brass doesn't expand as much, titanium doesn't expand as much, did my Z homing with the the bed already heated (145C). Not enough to add up to .25mm. Maybe the switch is really temperature sensitive and was sitting above the 145C bed for too long?