Myron L would be the only one I recommend and even then, I don't trust them 100%. I have never found one that does not need constant calibration and even with that, I see large swings that I have to verify with a liquid reagent test kit which by the way, cost a LOT less money and is always accurate. Since I have to keep the reagent kit around, I have opted to not purchase another meter with pH as the cost is just too high for what you get.