The drone climbed on entry. You arrived, touched nothing, and it rose a few metres and settled. Reported plainly, and easy to believe, because the number it was climbing to was written down in the code and was clearly the wrong one.

So the number got fixed. It was still wrong the next day, and the same number got fixed again.

The first fix was correct and sat in a line nothing reached. Entering flight does not go through the door I had assumed it did, so the corrected altitude was chosen, written down, and never asked for.

The second was correct and got overruled. There is a floor that stops the aircraft scraping the ground, and it sat above the height the aircraft was being told to hold. A floor you cannot fly under is not a floor. It is the altitude, and every other number is a suggestion.

Both times the constant read correctly to anyone looking at it. Both times the aircraft did something else. What was missing was not a better value, it was anything at all that watched the thing move and asked whether it had stayed where it was put.

That test exists now, and it is dull. Hover, touch nothing, measure. Across two towns and every spot that was checked, the answer used to be that it drifted upward every single time.

The general version of this is not about drones. A value you can read and agree with tells you what someone intended. It does not tell you what runs, and it does not tell you what wins when two parts of a system want different things. Only watching it move does that.