When the dry-bulb temperature is 22c and the wet-bulb temperature is 13c the relative humidity is?

How do you use hygrometers?

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 thermometers 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'. 6 Record the wet-bulb and dry-bulb temperatures. 6 Calculate the wet-bulb depression - the dry-bulb temperature minus the wet-bulb temperature. 6 Determine the relative humidity (%) using the table (reverse page). Read down from the wetbulb depression and across from the dry-bulb temperature. do's and don'ts Be careful with the instrument. The thermometers are made of glass and can easily break. Empty the water bottle before returning the hygrometer to its box. how it works The hygrometer works on a similar principle to the whirling psychrometer. The main difference is that the hygrometer is not rotated, so evaporation from the damp cloth around the wet-bulb thermometer occurs more slowly.