By coming into continuous contact with different pH values, the digital pH meter may lose its accuracy. It’s easy to tell when it’s time to calibrate. If the same water and the same preparation time are always used, the results are usually constant. If suddenly a water that is usually at a pH of 9.5 shows a pH of 8 almost in all cases, it is due to the bad calibration of the pH meter or the wear of its batteries. The device must be treated very delicately. The pH sensor is made of glass. It is located at the bottom of the pH meter that is submerged in the liquid, when not in use it is covered by a black cap. In case of breakage, the meter will no longer be able to fulfill its function. On the back of the pH meter there is a small screw that, when turned with the included screwdriver, adjusts the pH values during calibration. It is important to turn it very slowly to avoid over threading. To calibrate the pH meter, ONLY the fixed pH calibrant solution can be used and NEVER use other liquids with an approximate pH such as alkaline water with a pH of 9-9.5 PH-009 (I) pH meter Range: from 0 a 14 Resolution: 0.1 Accuracy: +/- 0.1 Batteries: 3 x 1.5 V AG-13 Life cycle: 700 hours Temperature: 0ºC~50ºC (Humidity: < 95%) Dimensions: 152 x 30 x 21 mm. < 95%) Dimensions: 152 x 30 x 21 mm. Includes calibrant powder sachet, calibration screwdriver and detailed instructions Weight: 51 gr.