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RH390-EU-EN V2.2   2/11 

Operation 

Power 

Press the power button(     ) to turn power on or off. 
 
 

Taking measurements 

1.  Hold the probe in the area to be 

tested. 

2.  Allow adequate time for readings to 

stabilize. 

3.  The Relative Humidity measurement 

appears in the top display.  

4. Pressing the 

°F/°C/WBT/Dew Point

 

button toggles the lower display 
between Temperature (°F), 
Temperature (°C), Dew Point (°C), 
Dew Point (°F), Wet Bulb (°C) and Wet Bulb (°F). 

 
 
 

Dew Point measurements 

1.  To select the Dew Point 

measurement, press the 

°F/°C/WBT/Dew Point

 button until 

DEWPOINT (°F or °C) appears in the 
lower right. 

2.  Dew Point temperature is now 

displayed. 

 
 
 
 
 
 
 

°C °F

Dewpoint

°C °F

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