If you’re a hiker or a backpacker, an altimeter can be a powerful navigation aid when used in conjunction with a map and compass.
Altimeters aren’t new, but they have fallen in price in recent years and are commonly included as a function in outdoor sports watches. For instance, I use a Casio Pathfinder Watch which has an altimeter (priced under $180) and is accurate to within 20 feet when calibrated. It’s completely transformed the way I navigate with a map and compass and has proven to be an indispensable navigation aid.
Here are a few examples of how an altimeter can help you pinpoint your location or guide you, both on-trail and off-trail.
Where are we along this trail?
Have you ever found yourself hiking up a trail covered by a forest canopy or lacking major landmarks and wondered how far you’ve hiked and how much farther you have to go? An altimeter can be used to pinpoint your location if you’re hiking in terrain with ups and downs and you have a topographic map handy.
For example, let’s say you’re hiking up the Black Angel trail, in the map above, which climbs several miles to the summit of of a mountain called Carter Dome. If you had an altimeter watch, you could check your elevation anywhere along its length to pinpoint your location on the topographic map.
For instance, if you queried your altimeter watch at point A, you’d see that the elevation was 3200 feet. Knowing that, you can trace your finger along the Black Angel Trail to 3200 feet on the topographic map, and you’ll be located at exactly that point on the trail. The same holds for point B, at 4000 feet.
Have we lost more elevation than we want?
While an altimeter can be useful if you hike on trails, it really shines when you step off trail because you can use it to figure out if you’re where you want to be or whether you’ve strayed off course.
For example, let’s say you want to hike from Big Bickford Mountain to Scarface Mountain, passing through the saddle between the two peaks at 2680 feet of elevation and following a compass bearing along the RED route. If you had an altimeter, you could check your elevation as you descend Big Bickford to make sure you don’t drop below the elevation of the saddle and off course. For example, if you found yourself at 2550′ feet, you probably fell of the RED route and followed one closer to the BLUE route.
This is quite an easy mistake to make when coming down a mountain, even if you’re hiking along a compass bearing. If you have to hike around fallen trees or other unexpected landforms, it’s easy to lose more elevation than you want. But checking your route with an altimeter as you hike can help you discover that you’re off course sooner and help you course correct faster.
We want to follow a constant elevation or contour around an obstruction.
The tops of many mountains are often covered with blown down trees and can be very difficult to traverse. One option is to avoid the blow downs by walking below the summit plateau at a more open elevation. Called following a contour, this can be difficult to do without losing elevation and increasing your energy expenditure to get it back, or climbing too high and losing speed amidst the obstacles you are trying to avoid.
For example, if you approach Sable Mountain, pictured above, from the north, one strategy for avoiding summit blow downs would be to climb the north ridge to 3200′ and to hike along the west-facing 3200′ contour until you get close to the actual summit on the south end of the mountain. The slope gradient below 3200′ is much steeper on the west face, so you wouldn’t want to drop below that elevation. However, side-hilling at a constant elevation can be tricky to maintain for any distance, and being able to refer frequently to an altimeter can be a big help in contouring around such a large obstruction.
The previous examples help illustrate some of the ways that an altimeter can be used for on-trail and off-trail navigation when coupled with a map and compass.
Most altimeters base their elevation measurement on the change in barometric pressue that occurs when you climb to a higher elevation or descend from one. Barometric pressure is also affected by changes in the weather, which can throw off your elevation reading if you don’t recalibrate your altimeter at least once a day.
Calibrating a barometric altimeter is quite easy, but it depends on knowning your exact elevation when you calibrate it. The best way to find your current elevation is to look it up on a map (if you know where you are) and adjust your altimeter by adding or subtracting elevation (feet or meters) to its current reading so that it matches the elevation of your current location. If you don’t know your current elevation, it’s best to hike to a known location on your topographic map and recalibrate your altimeter there.
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