Our Sling Psychrometer Kit is a simple hygrometer used in measuring the moisture content in the air. When spun around on their wooden handle the wet bulb thermometer and the dry bulb thermometer will read different temperatures. This information can then be used to determine relative humidity and dew point. Instructions included. Sold as a pack of 10 psychrometers. PRODUCT WARNINGS WARNING: This product can expose you to chemicals including nickel and lead which are known to the State of California to cause cancer birth defects or other reproductive harm. For more information go to www.P65Warnings.ca.gov. This product contains latex which can cause allergic reactions in some people. If symptoms of an allergic reaction occur stop use immediately and consult a physician. This product contains small parts making it a choking hazard. Only use with adult supervision. Our products are not toys. Use in a laboratory or educational setting only. Not for children 13 and under.