A Compass: What to Look For and Why

by Don Russell,

Map & Compass

Map & Compass

I’m sure it will come as no surprise to find that most people who purchase a compass rarely give it the depth of thought that one would expect. After all, you are buying a precision instrument that if treated properly will give many years of faultless service. It will assist in telling you where you are and get you to where you are going, it will tell you how far away things are and will also tell you the time. You can use it as a protractor and also as an inclinometer; it can even assist in removing splints and cleaning up cuts, but above all else, there will be times when you have to trust this instrument with your life. Let’s take a closer look at this instrument and what it is we require of it.

The Quality

There are many companies that make compasses but 99% of serious users will go for Silva, Suunto or Recta; their names synonymous with quality, accuracy, durability and reliability.

The Type

There are many types for different applications but if it’s for hiking, mountaineering and exploration a base-plate sighting compass is the type to go for.

Why a Sighting Compass

You can navigate accurately without a sighting compass but when you need to take accurate bearings for any number of reasons you will need a sighting compass. The accuracy of the bearings will be in the region of +/- 0.5 degrees whereas with a normal compass you are looking at +/- 5 degrees on a good day making any calculations almost meaningless.

The Base-Plate

The base-plate is the transparent polycarbonate plate on which the compass module sits. The base-plate should contain a ‘romer’ (the markings on the base-plate) these graduations will assist in giving accurate grid references and accurately plotting map positions along with time & distance calculations. It will have a magnifying lens to aid in reading the map more accurately when in mountainous terrain where the contour lines are much closer together. It will have 3 silicone feet to grip the map case while working and a lanyard fixing point with lanyard attached (this is always attached to your person in such a way that if dropped it cannot hit the ground or get lost… No exceptions).

The Graduations

This is down to personal preference and what you need to do. The choice is either degrees or mils, some have a combination of both. Many go for degrees because that is what they know and to be fair you can do all the same calculations with degrees that you can with mils; the difference being that with degrees you will need a scientific calculator with sine, cosine and tangent functions to complete some of the calculations, with mils, many of the calculations can be done mentally. In my experience the best set-up is degrees on the outer bezel with degrees and mils on the sighting disc; this way you can still use the rotating bezel as an inclinometer in degrees and if you require it in mils you can use the sighting disc to convert.

The Module

The compass module itself will be liquid filled; this ensures a silky glide to the needle and a well damped movement. It will be suitably engineered to ensure that it delivers the accuracy and reliability that is expected of a quality precision instrument. Make sure there is no bubble inside the module before you purchase the compass and that the needle glides smoothly to its position and stops quickly.

The Zone

For a compass to perform accurately the needle must be able to rotate freely. Due to the changing angles of the Earth’s magnetic flux in various locations the compass needle needs to be ‘tuned’ to the area in which it is to be used; this phenomenon is called ‘Magnetic Inclination’ sometimes referred to as ‘Dip Angle’ and it can deflect the needle so much that it drags on the module’s housing. The globe is split up into 5 zones; if you rarely go outside your zone buy a zone tuned compass. If, however, you are a global adventurer you can purchase a globally tuned compass for a little more money that will function correctly worldwide.

Illumination

When you advance to moving at night you will need to see the ‘direction of travel’ arrow, the compass needle and the rotating base markers; this illumination is best provided by ‘Tritium’. Tritium illumination needs no external light to charge it and is generally denoted on the compass by the three bladed radio-active sign. It has a half-life of around 15 years meaning that in 15 years it will only be around half as bright. This is normally extra but you should go for it; the reason being that if you have to keep shining your torch on the compass every half an hour it will play havoc with your night vision.

Protecting Your Compass

Compasses for some strange reason don’t generally come with a pouch. It is always best to protect any precision instrument from damage and you will find that various small mobile phone pouches are ideal.

Using Your New Compass

Learning to use your new compass is not quite as straightforward as it may seem. Knowing how to use the compass itself is only a small part of navigating; you also need to have a good knowledge of maps, grids and coordinate systems if you are to be proficient. When proficient you should be able to give your position to within 100m in hostile terrain and in almost zero visibility with a map & sighting compass. Even this does not make a good navigator, there is much, much more to learn.

Confidence

Learning to navigate has many advantages outside of the obvious one of finding your way about. It gives an enormous amount of self confidence, this overflows into all sorts of everyday things and it also keeps your mind sharp by doing the calculations. When this is combined with survival training you will be extremely happy to venture into places where others dare not tread. Navigation and survival seem to have been tagged masculine subjects over the years, mainly by the men I suspect; this coming about by the assumption that navigation and survival is all about pain and suffering… So females can’t be any good at it! The fact is that navigation and survival are both more intellectual than physical; if it’s all pain and suffering you need to learn more about it from a knowledgeable, patient instructor. It’s no walk in the park but it’s not a nightmare either. I suspect the real reason may be more about being shown-up by the girls than anything else. Sorry lads, I may have let the cat out of the bag here. Come on girls… Get out there and show ’em!

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