A hygrometer is a tool used to measure the Relative Humidity (RH%) of the air. The kind of hygrometer described here is specifically called a psychrometer. It takes a dry-bulb temperature reading and a wet-bulb reading. The technical specifics are complex; very briefly, comparing the two readings will tell you how much water vapor the air can hold.
To make your own hygrometer, you will need:
· Two identical thermometers
· A piece of cotton (gauze, shoelace, cheesecloth)
· Cotton string
· Foam-core or mat board
· Sharp knife
· Straight edge or ruler
· Awl or pencil, for marking cut lines
· Tape or twist-ties
· Drinking Straw
· Distilled water
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