Most handheld digital compasses employ a magneto-inductive method to measure the Earth's magnetic field. According to safety-devices.com, the magneto-inductive method used in handheld digital compasses can separate the Earth's magnetic field from other magnetic sources like natural magnetic iron deposits, and the weak magnetic fields around electrical devices. Handheld digital compasses give an accurate location and direction of travel by displaying the difference between true north (geographical direction) and magnetic north (magnetic field direction). Small handheld digital compass units are often used by mountain climbers, hikers, campers and soldiers when in the field. Handheld digital compasses are compact and able to withstand the rigors of hiking and mountain climbing.
Digital compass watches also use the magneto-inductive method to detect the Earth's magnetic field. The Digital Compass Watch website says that the digital compass watch is a combination chronograph and compass. In addition, they are easy to use and have large clear displays. Many different styles are available and most sport models are water-resistant. Digital compass watches allow the user to determine direction of travel by calculating the difference between magnetic and true north. The difference between true and magnetic north is called magnetic declination. When using a digital compass watch, calibrate the compass for magnetic north based on location. The National Oceanographic and Atmospheric Administration (NOAA) maintains a page to help hikers, boaters, mountaineers and travelers calibrate digital compasses.
Global positioning system (GPS) units have advanced rapidly in the last few years. Initially available only for military applications, the GPS has become an invaluable tool and standard equipment on many American automobiles. Handheld GPS systems are available for the hiker, mountain climber, boater and outdoor adventurer. According to the National Air and Space Museum website, the GPS receiver system calibrates location and direction of travel by receiving information from satellites that orbit the Earth. The receiver locates and receives position data from four or more satellites. Using the data it receives from the satellites, the GPS unit uses simple math to triangulate its location on the Earth. Handheld GPS units will indicate the exact location of the traveler in relation to known landmarks and the compass direction of travel.
