Milwaukee brand standard meter, which already gives you more confidence than conventional economic meters for little more than price. A meter that with its care will last for years. Put the probe in the nutrient solution and you will know the pH instantly on its digital display. Automatically compensates for temperature so you don't have erroneous readings. An inexpensive but effective meter. To calibrate it you will need a Ph7 calibration liquid and the help of the included screwdriver. We put the tip of the meter in the liquid and regulate with the screwdriver until reaching the level of Ph7. You can make it more precise if we regulate it later with liquid 4, but with 7 it will already have enough precision.