A pocket barometer is a handheld scientific device that measures atmospheric pressure, which can help predict short-term changes in the weather. Backpackers, hikers and other outdoors enthusiasts frequently use a pocket barometer to track prevailing weather conditions and to help plan their trips. Although a traditional pocket barometer would come in the form of a brass pocket barometer featuring an analog display, many modern pocket barometers are technologically advanced instruments with digital readouts. A pocket digital barometer often provides information on atmospheric pressure as well as temperature, humidity, the wind-chill factor and the ultraviolet (UV) index, a measurement of the sun's ultraviolet radiation.
Although conventional barometers had been in use since the 17th century, pocket barometers began to gain popularity in the 19th century, particularly in Great Britain. Advancements in technology allowed craftsmen to construct barometers that were smaller than conventional barometers and could operate without the use of mercury, which can be hazardous to the health of people if it is not handled properly. A traditional pocket barometer is designed so the barometer's pointer moves clockwise across a dial to indicate high or low atmospheric pressure. Certain models of pocket barometers manufactured in the 19th century are prized by collectors of antiques.
Many backpackers and hikers consider a modern pocket barometer an essential piece of equipment for a trip, along with items such as a pocket compass, a map, a knife, matches and sunscreen. A pocket barometer can be especially helpful for hikers charting a course in a mountainous region in which they could experience numerous changes in altitude. The primary consideration in reading a barometer is that rapidly declining atmospheric pressure indicates that weather conditions are about to take a turn for the worse, from mild and sunny to cloudy, rainy or snowy, depending on the location and its altitude.
A modern pocket barometer is often available in the form of a digital watch that offers various special features in addition to an atmospheric pressure readout. A digital barometer watch often includes an altimeter, a device that measures altitude. Hikers use an altimeter in conjunction with a topographic map to help confirm their location on a trip. Among other common features are an alarm that sounds to indicate a sudden drop in atmospheric pressure and a tool that tracks a hiker's rate of ascent or descent in feet per hour. Pocket barometers are available at outdoors shops and from specialty gear retailers.