I have a set of electronic scales. I don't use them very often, but had a succession of small things to weigh.
When you switch them on,m they autocalibrate.
However every time I put something on stupid weights cane up and the thing was drifting, so I started pushing the front panel buttons at random. Trying to remember how they worked. I managed to change it from grams to oz to qty of widgets. All to no avail.
The I rememberde I had a 100g calibration weight, went to get that, and realised the cover was still on the unit. It goes over the weighing platform
So I took it off and everything worked as it should.
Then when I had finished, I put the cover back on....
...and noticed it covered all the buttons I had been randomly punching...so I couldn't have switched the thing even on with the cover on.
I have just worked out what happened.
Can you?