Frostbite is the freezing of skin and underlying tissue from exposure to extreme cold, most often affecting fingers, toes, ears, nose, and cheeks. It progresses from frostnip (reversible numbness and pallor) to deep frostbite with hard, white or waxy, numb tissue. Refreezing thawed tissue causes severe damage, so rewarming should only be done when refreezing can be prevented.
Hypothermia is a dangerous drop in core body temperature below about 95°F (35°C), caused when the body loses heat faster than it can produce it — often from cold, wet, and windy conditions. Early signs include intense shivering, clumsiness, and confusion; severe hypothermia is life-threatening and requires rewarming and urgent medical care.
A pace count is the number of steps (usually counted on every other foot) it takes you to cover a set distance, typically 100 meters, used to measure how far you've traveled on foot. Knowing your pace count lets you track distance for dead reckoning and to find a target when you can't see it, adjusting for terrain that lengthens or shortens your stride.
Dead reckoning is estimating your current position from a known starting point by tracking the direction (bearing) you've traveled and the distance covered. Combined with timing and pace counting, it lets you navigate when landmarks are hidden — in fog, whiteout, darkness, or featureless terrain — though small errors accumulate, so it's checked against known features.
A grid reference specifies a location on a map using its grid lines, giving numbers read as an easting (across) and then a northing (up) — 'right then up.' Adding more digits increases precision, from a grid square down to a few meters. Grid references let you communicate an exact position quickly, including to rescuers.
UTM (Universal Transverse Mercator) coordinates locate a point using a metric grid, dividing Earth into zones and giving an easting (meters east within the zone) and northing (meters north). Because positions are in meters on a square grid, UTM is easy to plot and measure on a map, which is why many backcountry navigators prefer it to latitude and longitude.
A waypoint is a set of coordinates marking a specific location — a trailhead, junction, campsite, water source, or summit — saved for navigation. On a GPS or mapping app, you string waypoints together into routes and navigate from one to the next, while a recorded path of where you've been is called a track.
True north is the direction to the geographic North Pole, the reference maps are drawn to; magnetic north is the direction a compass needle points, toward Earth's magnetic pole, which lies elsewhere and moves over time. The angle between them is declination — accounting for it is essential to navigate accurately with map and compass.
Declination (magnetic declination) is the angle between magnetic north, where a compass needle points, and true north, used by maps. It varies by location and slowly over time, and ignoring it can put you significantly off course over distance. You correct for it by adjusting your compass or adding/subtracting the local declination from your bearings.
A baseplate compass mounts a rotating magnetic needle and bezel on a flat, transparent plate marked with rulers and direction-of-travel arrow, designed for taking and following bearings off a map. Its declination adjustment and clear base make it the standard navigation compass for hikers and mountaineers — and a Ten Essentials item that never needs batteries.