How to Use a Compass

Guide Note: Have you lost your way in life and are looking for some direction? Knowing How to Use a Compass can help you figure out where you're going and how to get there. Follow the instructions in this guide and you'll be on your way in no time!

Table of Contents:

Introduction

Photo courtesy of Wikimedia Commons
Photo courtesy of Wikimedia Commons
  • For over a thousand years, the compass has been used as a tool to help humans navigate their surroundings and orient themselves to the directional points on the globe. By simply adjusting the parameters of a compass, an individual can accurately determine their position relative to the four cardinal points. While the modern pocket compass has come along way from its humble origins (basically just a magnetized needle on a frictionless surface), the basic principles that govern its inner workings have stayed the same. Read on for instructions on how to use a compass so that you'll never be lost again!

How Does a Compass Work

  • In simplified terms, a compass works by using the Earth's natural magnetic field to attract the magnetized needle in the compass. Because of the magnetic attraction of the North and South poles, the North end of a compass needle will always point towards North pole and the South end towards the South pole. The exact reason for this is a little more complicated. Here are a few things that will help you better understand how compasses work:
    1. Think of the Earth as one gigantic magnet.
    2. As with all magnets, the ends of the earth have opposite polarities (North and South poles).
    3. As you may remember from Science class, "Opposites Attract" when it comes to magnetic polarities.
    4. Because of this, the points of a compass needle need to have an opposite polarity to the direction they are supposed to indicate.
    5. So, the North end of the compass needle (with a southern polarity) will be automatically attracted to the North end of the Earth's magnet.

Parts of a Compass

Photo courtesy of Wikimedia Commons
Photo courtesy of Wikimedia Commons


  1. Compass Needle: The magnetized needle that is used to determine which direction is North. The Red end of the compass arrow will always point towards the Earth's magnetic North pole.
  2. Compass Housing: Houses the needle in a fluid-filled, frictionless capsule. Can be rotated manually to line up with the compass needle in order to take a bearing.
  3. Orienting Arrow: The indicating arrow that is used to help align the compass housing with the needle.
  4. Direction of Travel Line: The indicating line that it used to determine a bearing once the compass housing and needle have been aligned.


How to Take a Bearing

  • The most basic function of a compass is the ability to take a bearing - In other words, to determine the direction that you are traveling. If you're lost in the woods and you know that you've been traveling south, simply use your compass to take a bearing and determine which direction is North - and then follow that bearing until you reach civilization. Or if you just want to figure out which direction you are currently traveling in, go ahead and take a bearing to find out. Here is how to go about taking a bearing:
    1. Hold your compass flat on your hand.
    2. Adjust your position so that the Direction of Travel Line is pointed in the direction you are currently traveling (or any other position you want to take a bearing). The compass needle will automatically adjust to the changing position of the compass.
    3. Adjust the Compass Housing (by rotating it manually) so that the Orienting Arrow is perfectly aligned with the Compass Needle. Note: Remember that the North end of the compass needle should line up with the Arrow.
    4. Take a look at where the Direction of Travel Line matches up with the bearing markers on the Compass Housing and take note of the degree marker. This is your bearing.
    5. If the Direction of Travel Line falls half-way between North and West, then your bearing is "North-West", half-way between East and South and your bearing is "South-West"...etc.

How to Use a Compass with a Map

  • While compasses are often used to simply take a bearing, they can also be used in conjunction with a detailed terrain map to help you determine which direction you need to travel in order to get from one point to another. When traveling in unfamiliar wilderness areas, having a map to help you plot your bearings is essential. Here is how to your map and compass to get you where you need to go:
    1. Lay your map out on a flat surface.
    2. Find and mark two points on your map: Where you are starting from and where you want to go.
    3. Place your compass on the map so that the long side of the compass connects the two marks you made on the map with a straight line. Make sure that the Direction of Travel Line is pointing in the direction you need to travel.
      Photo courtesy of Wikimedia Commons
      Photo courtesy of Wikimedia Commons
    4. While holding the compass firmly on the map, rotate the Compass Housing so that the North-South orientation lines on the housing are parallel to the North-South lines on your map.
    5. Now take the compass off the map and hold it flat in your hand with the Direction of Travel Line pointing out.
    6. Rotate your body (with the travel line pointing outwards) until the Compass Needle lines up with the Orienting Arrow.
    7. Once the two are aligned, the position that the Direction of Travel Line is in will tell you which direction you need to travel in order to reach your destination.

How to Set the Declination Value

  • In order to get a truly accurate reading from your compass, you will have to account for something known as Declination. In order to understand declination, you must first come to terms with the fact that there are actually Two North poles: The "Geographic" North pole (which is a physical location at the Northernmost point on the globe) and the "Magnetic" North pole (which is a result of Earth's changing magnetic field).
  • While both poles are in relatively the same location (at the top of the Earth), because of the constant shifting of the Earth's magnetic field, the exact location of the two can often differ by anywhere from 500 - 1000 miles. Since your compass needle will only point towards "Magnetic" North, in order to get a true bearing on "Geographic" North, you will have to account for the difference. This difference (usually calculated in degrees) is called the Declination Value.
  • In order to calculate the declination value that you will need to account for you can:
    1. Go to this handy website from the National Geophysical Data Center (NGDC) and enter in your specific data in order to automatically calculate the declination value of your location.
    2. Consult a declination map (such as This One) and find the declination value of your location on the map. But since declination values can change, as This Image shows, it is important to the most up-to-date map available.
  • Once you've determined your declination value, you can then apply it to your calculations:
    1. Declination values are expressed as either positive or negative (i.e. -20 degrees or 20 degrees) - where a negative value represents a Westerly declination and a positive value represents an Easterly declination.
    2. If your current declination value is -20 degrees, then that means that the reading on your compass is 20 degrees higher than it should be. If your declination value is 20 degrees, then the reading on your compass will be 20 degrees lower than it should be.
    3. In order get an accurate reading, simply adjust your compass reading so that it accounts for the declination value. (i.e. If you want to plot a course for a 60 degree bearing and your declination value is -20, simply add 20 degrees to your compass reading (making it 80 degrees) to compensate for the difference.

Conclusion

  • While the emergence of sophisticated global positioning systems (GPS) have relegated the use of compasses to mainly outdoor enthusiasts, Boy Scouts and orienteering specialists, knowing how to correctly use a compass is still a skill that can come in handy in the right situation. And although the physics behind magnetic fields and how a compass works may be hard to fully grasp, the accuracy of their readings and their ease of use is the reason that they have been such a trusted navigation tool for so long. So the next time you're out camping in the wilderness and are wondering which way to go, just break out your trusty compass and let the Earth's magnetism lead the way!

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