I would track your own progress with what ever means you think you can consistently measure. I have marks on a pumping tube that confirms growth (same pressure). So do what you want, but be consistent.
As far as bragging to girls, then I would say you can use whatever cheating measurement you think you can get a away with, as long as you can back it up. For instance, if I had to measure in front of a girl or wife, I would use a tape measure on the side and follow my curve. Ooopps, that is at least 3/4” longer than a true meausrement, but who cares?.