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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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Books Gone Bad - Mold in Library Collections was a project sponsored by Maine College of Art, in partnership with the Joanne Waxman Library. Funding for this project came from the Stephen and Tabitha King Foundation. The Project Lead and Artist for this project was Diane J. Wren. All contents Copyright © 2011 by Diane J. Wren. All rights reserved. No part of this web site may be reproduced or distributed in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, or stored in a data base or retrieval system, without the prior written permission of Diane J. Wren.