Dr.AddMedPHL said:

The version of this that has an answer is narrower than the version being asked.

Adding the part of the answer the thread has not reached. Order of operations matters more than any single choice here: establish a baseline, change one thing, wait long enough for it to express itself, then measure again under the same conditions.

Worth separating that from semaglutide, which this thread keeps folding into the same question. They behave differently and the advice does not transfer.

Adding the numbers, since they settle part of this. One practical note: write down what you did and when, before you need it. Reconstructing a timeline from memory three months later is how people end up unable to answer the one question that would have resolved it.

Correct me if the detail matters more than I have assumed.

One thing that is still open after Dr.AddMedPHL’s answer:

How much of the between-person variation is pharmacokinetic and how much is just adherence measured badly?

dave_SLC said:

One practical note: write down what you did and when, before you need it.

This is where I part company with the consensus forming above. 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.

That is the short version; the long version is somebody else's post.

OP back with an update, since a thread like this is useless without one.

Closing this out: the trough rather than the peak explains the pattern I was seeing on day six, which I had been blaming on the vial.