Good question, Jon. I don't have an answer, but if your Rapitest meter is anything like mine, it will register 7.0 every time, on every soil. ;)

fortyonenorth,

I did spend a little more and got a digital pH meter, and followed the directions last year to the T, and think I got fairly accurate results when compared to the chemical tests as well. I was able to confirm that my berry plants did have a lower pH than my peppers and tomatoes. However, with all the horror stories, I do use the pH meter was well as the chemical test. Other than spending big $ on a pH meter, this is sufficient for my interest.
This year however I am using a bark based mixed, and am curious as to the best method for testing the pH, if for nothing else, just to get a general idea when the pH starts to climb, because I know our water here has a fairly high alkalinity which does cause the pH to rise over the growing season.

Jon,
I would simply soak some mix with distilled water, wait a few minutes, then pour out some
of the water and test it. That'll give you a reference point. The actual pH of the mix,
as you know, is less important than the pH of the fertigating solution.

Josh