When preparing for a print job I re-levelled the bed and all seemed OK, then the sun came out and the next auto-home was low, so I shielded the printer and the next home was nearer. I then turned the lights off in the printer and the home level changed again but almost recovered when the lights were turned on again. The differences were not very big but around 0.1mm in the worst case, so will have a real effect on the first layer performance. It seems that any source of light is going to have some small effect on the sensor so I am going to try shielding the sensor with tape and try a strip of tape on the bed in the home area to see if the effect is repeatable. I'll update later. I was wondering if anyone has fitted the inductive sensor yet and has any results. I know that @Alex9779 has one to fit but I may have missed the reports.