TinaHashiRN said:

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…

Right, and the exception is worth naming rather than left implied, because the exception is where people get into trouble.

FranDenver said:

Correct, and worth adding that it is reversible.

Thank you for spelling out the reasoning rather than just the conclusion.

TinaHashiRN said:

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…

Careful with the causal language. Two things moving together in a period when five things changed is not a mechanism, and stating it as one makes the thread less useful to somebody reading it later.

Adding the numbers, since they settle part of this. 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.

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.