Review on Rechargeable Digital Water pH Meter with ATC - High Precision 0.01pH Resolution Tester for Hydroponics, Aquarium, and Lab - Measurement Range 0~14 pH by Ryan Gillett

This is one of my bad buys from Revain and it makes me sad 😥 Instructions or lack thereof are not at all clear. Upon receiving and opening the product, it looked like it had been used before. I did a simple calibration. Add one packet to 250 ml RO water. I prepared all three (4.00, 6.89, 9.18) in different 250ml cups. Stir with a spoon (RO clean), let stand and dissolve. Mixed again (OO clean). I cleaned the RO tester and placed it in a 6.89 solution. Not even close. I put the calibration back into the 6.89 solution and after blinking three times I read the calibration. Went back to solution 6.89 and got a satisfactory reading. RO rinsed the tester and put it in a 4.00 solution (it should read 4.00 correctly), it didn't come close at all. It's not worth the price.