Sutro measures three parameters:
The pH is measured with phenol red (the same thing you would have in your liquid test kit), and it's range is between 6.8 - 8.2 (+/- .1 pH)
The free chlorine is measured by DPD, and it's range is between 0 - 5ppm (+/- .2ppm).
The alkalinity is measured through a titration method. This method is proprietary to Sutro, because we titrate such small amounts of it, but the range is between 40 - 250 mg/CaCO3 (or ppm) (+/- 20ppm).