I have one that measures to the hundredth. It's an electronic instrument. You can get a cheap one for a couple hundred dollars. I will tell you that I rarely use the electronic one now I almost always use the K-1000 in the TF-100.
A pool is not a static display - it's almost alive. The water level changes with evaporation and splashout, so the volume changes; just moving the water tends to make pH rise. Even the temperature changes through the day can affect pH. All you need to do is keep it in the comfort range, which the color match test can do fine.
I appreciate the response, but all of the tests we perform are a snapshot at that time--nothing more. The levels that pool school recommend for me are not a constant on the color chart. In fact, they are in the level range below-- and I would like to know just how far off I am. Maybe I am lucky in the fact that my PH seems to be a constant, regardless of my SWG. Just trying to perfect the system as close as I can.
I hope that makes sense, as it has been a long day!