These days, it seems like everyone has a smart phone, and knowing your location is as simple as pulling up Google Maps.
But what if that’s not the case?
What if you are in the woods and your phone runs out of battery, or worse, jumps off a cliff?
What if the GPS network decided to deorbit itself and nothing but stars and planets light up the night sky?
What if you have to navigate without using an app?
The horror, I know. Fortunately, there are ways to figure out your location without relying on GPS.
Ancient civilizations navigated using the stars, but we have a technological edge on them.
An edge which does not require you to be constantly connected to the internet.
A watch. Specifically, an altimeter or ABC watch.
I guess you may want a compass as well.
No, these watches do not teach you the alphabet. In addition to telling the time, they show you data about your current location using what’s in their name. Altimeter, barometer, compass.
What is an Altimeter?
The further up you go, the less air is above you, so the less atmospheric pressure presses down on the barometer. The device does some calculating, and outputs your elevation. Easy!
Types of Altimeters
There are a few types of barometric altimeters in use nowadays.
I suppose if you want to do things the hard way, you can fill a glass container halfway with water, curve it, and expose one end to the outside through a tiny hole. Measure the height of the water and perform some fancy calculations to figure out your altitude.
On second thought, let’s go with something easier.
Aneroid barometers function as altimeters, and work by measuring the expansion and contraction of metal, typically beryllium or copper. As nifty as they are, you probably will not use one of these unless you’re flying a plane.
What you are probably most interested in is the digital barometer. They are basically a sensor that measures air pressure. These are what you will find on your ABC watch.
Since you can use one barometer for both altimeter purposes and for generic atmospheric pressure data, you could probably call ABC watches BC watches, but then everyone would look at you funny. Weirdo.
We just call them altimeter watches anyway.
You can also purchase stand-alone altimeters, without the wristwatch bit. Some include elevation logging and other tools, while others are nothing but an altitude measurement.
GPS may give you your altitude, but it is not an altimeter, and it may be unwise to rely on GPS to know your altitude.
At best they are not-quite-as-accurate as a properly calibrated barometric altimeter. The measurement gets worse as the satellite angles get closer to the horizon.
Even worse, you can lose GPS signal and receive no measurement at all!
Who Uses/Needs an Altimeter?
Skydivers and pilots have very pressing needs to know their altitude.
For people on the ground, altimeters are useful for two types of people.
The first type of person is someone who likes to keep track of their changes in elevation for hobby or bragging reasons, such as skiers, and rock climbers.
The second group of people is those who put their lives at risk if they do not navigate successfully.
Even people driving through the wilderness can sometimes find themselves in this category with little warning, and since many ABC watches have long-lived batteries or solar cells, an altimeter watch can save your life when your phone dies.
Why Is It Useful?
At first glance, knowing your exact altitude does not seem much more than hobbyist information. But there are life-or-death applications.
When matched with a compass, an altimeter lets you navigate using a map much more accurately than by compass alone.
Mountain climbers often need to know their rate of ascent. If you are climbing a mountain and the closest safe place is so many feet above you, by keeping track of your altimeter you will be able to easily figure out if you can make it there before night fall.
Also, since altimeters are barometers, they can help inform you of a sudden storm before it becomes too late.
How to Read an Altimeter
Most modern digital altimeter watches are dead easy to read numerically display your altitude in meters or feet, your choice.
I would recommend making the choice to match your map, not personal preference.
Analog altimeters are a bit more complicated. They have a face like a clock, with a needle swinging around to point at the altitude measurement.
More accurate analog altimeters will require multiple revolutions to measure large changes in altitude, or will have separate dials for the fine and gross altitude measurement.
A compass reigns king for helping you navigate with or without a map, but an altimeter is queen for making your map reading skills much more accurate.
If you have a topographical map and an altimeter, you can combine the altimeter reading with the elevation lines on the map to determine your exact location.
Helpful if you are on the trail, this can keep you from making costly mistakes in navigation off the trail.
If you are navigating through mountainous terrain, you can check to make sure you have not lost or gained more altitude than you had planned for your route. Changing more elevation than necessary increases your energy expenditure and slows you down.
When traversing a mountain you may want to keep a constant elevation by following the contour. Keeping track of your altimeter can help make sure you are not veering off course.
It’s important to keep in mind that because the altimeter watch is affected by weather, every measurement is an estimate. It can be a very accurate estimate, but do not stake your life on it.
Calibrating an Altimeter
Altitude is not the only thing which changes atmospheric pressure.
The weather can have a large effect on your barometer’s measurements, and because of this you should calibrate your barometer/altimeter at least once a day by changing the displayed altitude to match your own. Trail heads and base camps often give their specific altitude for this purpose.
Topographical maps can also be used to figure out your precise altitude if you know where you are on them, and you can use internet maps to figure out your starting elevation at, say, your house.
Altimeters and Weather Prediction
Because altimeters are barometers, and barometers are affected by the weather, your altimeter can help you predict the weather!
Your altimeter watch may give you the atmospheric pressure as well as the altitude. Some even have built-in weather prediction functions.
But even if all you can see is the elevation, by remaining stationary you can have a rough guess at the weather.
Altimeter change is the opposite of barometer change; as air pressure drops the displayed altitude increases, so you can use any barometer recommendations so long as you invert the verb.
If you are staying at one elevation but the altitude is rising, that may indicate an approaching storm. Conversely, a dropping altitude probably means more air pressure, and thus clear weather.
A slow change is a long term weather change, while a sudden change signifies weather that will arrive and depart quickly.
With an altimeter, a compass, a map, and a bit of navigation practice, it will be nearly impossible to get lost. An ABC watch supplies two of the four elements, without relying on satellites or short-lived smart phone batteries to get you through the trouble.
Plus they look much classier than a smart watch.