The figures, for anyone assembling their own picture. Practical: whatever you change, write down the date and the reason. In three months the reason is what you will have forgotten, and the reason is what makes the record worth having.

Ask again with the specifics and you will get a better answer than this one.

One thing that is still open after jim_asheville’s answer:

What did you change at the same time, and can you separate the two now?

Dr.PathRoch said:

Practical: whatever you change, write down the date and the reason.

Filing a mild objection. Mild because I might be wrong; an objection because nobody has addressed the case that does not fit. The objection nobody has made: this only works if the measurement is doing what we assume it is doing, and that assumption has not been tested here.

Dr.PathRoch said:

Practical: whatever you change, write down the date and the reason.

That holds where the measurement is reliable. Where it is noisy — and a lot of what gets tracked here is noisy — the same reasoning produces confident nonsense.

Dr.PathRoch said:

Practical: whatever you change, write down the date and the reason.

Genuinely useful, thank you. I had the facts and not the framework. Printing the relevant bit and taking it with me.