This is the one I got and it is great. The one I had was undependable It would not hold calibration. I had to check and calibrate it every time.
This one, calibrate it once and then the machine will tell you if the calibration is off. It is a little expensive ($45) but is fast and compares and reads the same as another meter a friend has that is $200. He works in water purification. I like it !