1. Once the meter is on, the temperature function can be used at any time, in or out of liquid. 2. Press the TEMP button. The display will switch to temperature (in Celsius only). 3. To return to TDS mode, press the TEMP button. This item can be used to test TDS in water purifiers and filters. Precautions 1. The meter is not water-tight. Do not dip the meter beyond the water level limit. 2. Do not store the meter in high temperatures or direct sunlight. 3. Do not attempt to open the housing or tinker with the electronics of the unit.