I had been having minor issues with the repeatability of levelling between one job and the next; not too much to affect the job but noticeable. After a recent re-levelling and going to store the results, I held the button down longer than I had normally done and was rewarded by a very small bleep from the buzzer; since then I have had no problems with the bed being out of calibration despite multiple restarts. I noticed that this bleep occurs on the read memory function too, so I am wondering if this feature(?) is part of the Marlin firmware? I am not smart enough to delve into the firmware but if someone out there knows the answer, it would be nice to know. I am using @Alex9779 's latest firmware on my hybrid dual with a red PEI on aluminium bed with the IR detector pointing to a small black ink patch on it in the home position. I raised this because earlier information said that there was no response from Marlin to let you know if the store/read had taken place.