[Kodak]

Weights and measures periodically tests pumps. I'm not sure how often. Each pump has to be within a certain fill variance (+/- X%) to be certified. You should see a sticker on the pump.

I logged one tank a while back came out to a bit over 24mpg before I was even capable of doing 23 consistently, so I suspect filling variance played a role.

Maybe one pump is a bit generous, and the other is a bit shy.

Try to fill at the same pump, but personally I wouldn't idle waiting for a specific pump unless you have a pressing reason for needing a precise number.

As an added tip, try to take note of which pumps are the most popular, and pick a lesser-used pump as your favorite (unless you suspect it pumps a bit shy of a gallon).