Fill the water bottle and screw it on to the instrument. Then hang the hygrometer (by the loop at the top)
on a wall or a tree, for instance, for at least five to 10 minutes before taking the measurements.
Ideally the instrument should be in a well-shaded spot or in a Stevenson screen (refer to Making your own
weather station in Section 4: Contacts and further information).
The instrument contains two alcohol-in-glass thermo-meters with a scale of minus 10 to plus 110 degrees
Celsius, in 1 degree increments. The end of the wet-bulb thermometer is covered with a damp cloth dipped in water. The other thermometer is the dry-bulb.
- Record the wet-bulb and dry-bulb temperatures.
- Calculate the wet-bulb depression. This is the dry-bulb temperature minus the wet-bulb temperature.
- Determine the relative humidity (%) using the table (reverse page). Read down from the wet-bulb
depression and across from the dry-bulb temperature.
|
