The Hanna Instruments HI 9813-6 Portable pH/EC/TDS/Temperature Meter with CAL Check Feature is a versatile, water resistant, multipara meter portable instrument specifically designed for agricultural applications such as hydroponics, greenhouses, farming and nurseries. It features a large LCD that clearly displays the parameter being measured as well as calibration instructions. Calibration is fast and easy with knobs located on the front panel of the instrument. CAL Check allows the user to easily check the pH probe calibration status at any time.