A Magnetic compass is an essential piece of any ones hiking gear, beginner or experianced, it should always be carried with you.(together with an area correct Topographical map)
Learning how to use the compass is as important as carrying it, and for those who do not use a compass frequently enough to remember how, its worth keeping some brief notes some where in your pack to remind you when required.
How does the Magnetic Compass Work
The Compass needle is a small piece of magnetised metal – a magnet.
Every magnet has a North and the South end,(called poles) while the opposite poles will happily attract each other, the same poles will strongly repel. In the most simple terms all this attracting and repelling creates magnetic field of “attraction” around the magnet.
The Earth is essentially a big magnet with North and South Pole magnetic poles, and a magnetic field that likes to attract opposite poles.(The earth also has two virtual Geographic poles which mark its axis of rotation in orbit.(*1))
The Compass needle always points in the direction of the earths own magnetic field and towards the opposite(*2) (and attracting) magnetic pole, regardless of where you are facing on the planet.
Why is the compass more reliable than GPS?
The compass is effectively “powered” by the Earth’s own magnetic field,(*3) and only one thing can cause it to error: You. The GPS however is dependant on a much larger list of variables;
- Adequate battery power and functioning hardware /software
- Adequate signal / Satellite coverage
- Calibration state of the electronic compass (depending on the GPS type and other conditions, some need regular field calibration.)
- Electronics surviving the outdoors conditions you are operating in and or falls.
- You realising when the GPS is suggesting you walk off a cliff.
- You being aware of all the variables and “checking the GPS’s work when things don’t seem right”
Best Magnetic Compass for Hiking?
The Magnetic compass comes in many different types depending on intended use, however the best kind for hiking is the Base Plate Compass.(*4)
- Base Plate: This is made of clear plastic so you can continue to see the map you are working with at all times.
- Rotating Housing: The central rotating circle attached to the base plate in which the compass needle sits.
- Dial: This ring on top outer edge of the rotating housing,(*5) which indicates the direction in Degrees of a Heading or Bearing, as well as the location of the Cardinal Points of the compass.
- Direction of Travel Arrow: Marked on the base plate, this points away from the compass housing in the direction to you will be walking.
- Orientating Arrow: This Rotates with the housing, and keeps the compass orientated to Magnetic North.
- Declination Marks: Present on some compasses to assist with calculating the Magnetic Declination when navigating with a map and compass.(the angular difference between Magnetic and Grid/True North)
- Orientating Lines: These red and black lines run parallel to the Orientating Arrow and are used for orientating a map to the north before use.
- Needle: Sitting in the movement dampening fluid capsule, the red tip indicates Magnetic North, while the white indicates South.
- Scales: Useful for calculating distance while working with a Map. A small ruler and usually a 1:50 scale are usually present.
What can a Compass do?
On its own a Magnetic compass is pretty limited to;
- Pointing to magnetic North, and defining the position of the other Cardinal compass points: South, West and East.
- Defining the position of a Geographic feature(like a hill top, tall tree..) relative to Magnetic North.
- Assisting you to walk a straight line to a selected visible destination, and then retrace your steps if required.
- Can be used as a protractor…
The true potential and value of a Magnetic Compass is only realised when it is combined with a Topographic Map. (to be discussed in future posts on the subject)
The Earths magnetic field is relatively weak at the surface, so any metal or magnetic field in close proximity to a compass will cause the needle to read incorrectly. This is know as Magnetic Deviation,(*6) Common causes of include;
- Metal objects like: belt buckles, wrist watches, buttons, roofing iron, steel posts, camping equipment…(attract magnets)
- Over head power lines, power transformers, power cords, electronic devices, particularly Smart Phones, Audio speakers, GPS units.(electromagnetic feilds / magnets)
With this in mind it is always wise to ensure your Compass is away from sources of Deviation to prevent it becoming damaged, both while hiking and when at home.
I carry my compass in my map bag against my chest, in easy reach and well away from my phone and stove/ camping equipment.
Buying a Compass
Before we go any further with how to use a Magnetic Compass, the first step is to buy one and get familiar with its features.(*7)
In addition to the all the standard part of a compass, there are some optional extras that are worth considering when you buy your Base Plate Compass;
- Magnifier: Usually located halve way up the direction of travel arrow on the base plate, this is very handy for reading small detail on Topographical Maps.
- Declination Scale: Printed on the base of the housing, which allows once calculated for you to set the declination for your region once.
- Luminous Components: Particularly on the compass needle and direction arrow, which are pretty handy in bad light
- Lanyard Hole: A little hole , usually at the rear of the base plate, all thought you can always drill one your self.
- Compass V GPS
- The different types of Compass
- Parts of a Magnetic compass
- Buying a Compass REI
- How Magnets work
- How does a compass work
- Geographic North pole v magnetic north pole
- Magnetic Deviation
(*1) The difference in angle between the Earths Magnetic and Geographic poles is known as the Declination. (also know as Magnetic variation) Calculating this angle becomes important when we start Navigating with map and compass.( I will cover it in a future post)
(*2) Yes the compasses North arrow seems to be pointing to the Earths North pole, which means it should really be repelled! (similar magnetic poles repel) But there is a trick here, the Earths North magnetic pole located in the Arctic circle, is actually technically the South Magnetic Pole, and there for attracts the North magnetic pole of the compass needle.
(*3) Unless you are navigating some where close to the Magnetic Poles (Antarctica or Arctic )… The one place on Earth where the Magnetic compass is totally useless…
(*4)Some prefer to use the Prismatic Compass, because it has a mirror that shows the compass needle even when you are looking a head on your course, but it is not designed to be used with a map like a Base plate compass.
(*5)Often also called the Bezel or Azimuth Ring depending on where you are from.
(*6) Compass that are installed in vehicles and ships where there is a lot of metal and wiring are corrected for Magnetic Deviation on installation so they still work.
(*7) The owners manual should be pretty good for learning its features, but also check out the manufacturers website for more information.