These highly accurate altimeters measure altitude up to 15,000 ft or 5,000 meters. Analog altimeters are battery-free, low cost, and often more accurate than a GPS receiver for measuring altitude. A SUN altimeter, used along with a topographic map’s contour lines, can help you determine or verify your location. Your SUN altimeter will also help you track your location in foggy conditions, when it’s difficult to use compass and landmarks to determine your position.
It’s important, since weather-changes affect atmospheric pressure–and so the reading on your altimeter–that you reset your altimeter needle often, at points of known elevation (for example, from elevation signs you see, your topographic map, trailhead elevation markers, etc).