Review on 🌊 KETOTEK Digital PH Meter: Accurate 0.01 PH Pen Tester for Water, Hydroponics, Aquariums & More by Gary Shakeone

This gauge cannot be calibrated. I'm not new to using/calibrating pH meters. I used the attached solution which didn't work and also used my own solutions. You would expect some margin of error with this type of product, but after all calibration attempts it showed a pH of 7.5 with apple cider vinegar, 9.2 with white vinegar and 11.5 with distilled water. My baking soda solution had a value of 2.8! These types of gauges are never entirely accurate, but you should be able to calibrate them accurately enough. Litmus paper is cheaper and better than this thing. If you buy this device or any other similar device, be careful if you need reasonably accurate readings. Many people need pH values for aquarium water, household cosmetics and the like. A defective meter can cause serious problems. Especially in cosmetics where pH measurements are crucial to determine the type/amount of preservatives.