In my 16 years of doing my own tanning I have purchased almost that many PH testers. After having a hard time getting anything done about the Oakton tester I bought late last summer that wouldn't calibrate I decided to try something different. I bought a Milwaukee model MW102 P/H / Temp. meter the first of December. I am Very happy with it and feel I can trust its readings. Very easy to operate and it has a 2 year warranty, price not much more than the Oakton #10 tester.