I'm very curious about this topic because I've heard many different types of measurements coming from formulators. I particularly prefer to use the pHmeter directly in the finished formulation. I don't really like the pH strips because they are not very accurate, but they do their job when needed. On the other hand, I've seen reports of people doing solutions to check this... but what would be the scale/proportion of that?
Are there other methods you know of? Which ones do you use? Help a curious one!