To use a Sling Phycrometer you dip one of the thermometer into water to get the Wet-Bulb, to get the Dry-Bulb you just leave the other thermometer as is. Then, you do 3 trials each for about a minute. Last, after each trial record your data and use the Humidity Cauculator (instructions on how to use below) to get the Relative Humidity.
A Sling Phychrometer measures: Relative Humidity, and Dew Point. To get Relative Humidity, you need to use a Humidity Cauculator ( see above ). To use a Humidity Cauculator, First, you take the Dry-Bulb and Wet-Bulb. Then, you find the two temperatures you recorded with the Sling Phychrometer on the Humidity Cauculator. Lastly, you use your fingers to folow the columns of the two temperature numbers and you have the Relative Humidity.