The meter has been used for a long time since the last calibration or use.The meter has been used under particularly continuous conditions.Do not press the button for a long time "Temp/Cal" at ordinary times, otherwise the meter needs to be recalibrated.The water quality monitor is a professional and useful tool for testing the level of PH/EC/TEMP solution /TDSIt looks like a pen, which is perfect for carrying. Excellent for various use, such as drinking water, aquariums, laboratories, water quality monitoring, swimming pools and so on. Product Description product Characteristics: Range pH: 0.00 ~ 14.00 PH. EC: 0-1999 us/cm 0-19.99 ms/cm. TDS: 0-1999 ppm 0-19.99 ppt. Resolution Temperature: 0 to 50C. PH 0.01PH. CE: 1 us/cm (< 1999 us/cm), 10 us/cm (> 1999 us/cm), 0.01 ms/cm. TDS: 1 ppm (< 1999 ppm), 10 ppm (> 1999 ppm), 0.01 ppt. Temperature: 0.1C. Accuracy pH: 0.02 PH. CE: 2% F.S. TDS: 2% FS. Temperature: 0.5C. Automatic temperature compensation: 0C to 50C. Battery type: 3 1.5 V (AG13). Operating temperature: 0C to 50C. Calibration: two point (4.01, 6.86) or one point (6.86) calibration Automatic shutdown: after 8 minutes Dimensions: 188 x 35 x 35 mm. Weight: 98 g.