"Fellow travelers will be glad you brought along this handy device from Brunton. This atmospheric data center displays your altitude (to 30,000 ft.), wind speed, temperature, wind chill factor, time, and barometric changes that have occurred over the last 16 hours. Hangs conveniently from lanyard. Water-resistant case. Uses 3V lithium CR2032 battery, included. 4 x 1¾""1.8 oz. Closeouts. Switzerland."