A narrower follow-up, since the general answer is now clear:

Was that from a primary source or from a summary of one?

DanielChem_CHI said:

The boring version of this is the one that works, and the boring version is: measure a baseline, change one variable, wait, measure again under the…

This is where I part company with the consensus forming above. The counter-case has not been addressed. Somebody upthread described the situation that does not fit, and the thread moved on rather than engaging with it, which is the failure mode this board is supposed to avoid.

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

Moderator note: the sourcing question belongs in the vendor section and has been split out. No action needed from anybody.

DanielChem_CHI said:

The boring version of this is the one that works, and the boring version is: measure a baseline, change one variable, wait, measure again under the…

This is exactly what I could not find anywhere else. I will report back once I have actually tried it.

Clinical perspective, offered as context rather than as advice. Whatever the answer turns out to be, the method for getting there is the same: state the assumption, do the arithmetic in public, and invite the correction. That is slower than asserting, and it is the only version that survives being wrong.