Compasses

compass face

Despite the advent of GPS units and smartphones with Google Maps, it still pays to carry a compass says Judy Armstrong, who tests four of the best

A compass might seem old-hat compared with the advancing technology of camera equipment and GPS devices, but team it with a map and a modicum of knowledge, and you have a go-anywhere system. Once youbeen on a mountain in bad weather and low visibility with a GPS whose batteries have died, youlook upon your compass in a new light.

There are several types, although relatively few manufacturers. The most common is the base-plate compass, with variants based on size and features. These include mirrors, romer and map scales, anti-slip feet and rubberised bevels. Sighting compasses, which include a mirror, are a little bulkier but more accurate over distance.

Digital compasses are as rare as handhelds, but are often incorporated into multi-function watches. The Suunto Core, tested here, is an excellent example of an ABC (altimeter, barometer, compass) watch, providing a digital compass function among other features.

The key thing to remember with a compass is that, while paper maps point to true north, compasses point to magnetic north. Because these are not the same location, you must set the declination —the angle between magnetic and true north, also called magnetic variation —on your compass in order to get a truly accurate reading. Declination also changes slightly over time. There is actually a third factor —grid north, which varies minutely from true north because of the inevitable limitations of making flat maps. For rough course settings you can ignore these differences, but for detailed navigation you need to adjust accordingly.

TOP TIPS

» Some compasses allow declination to be set and held; others must be adjusted for each use. A useful website for determining declination for a specific time and place is www.magnetic-declination.com

» Romer scales are a right-angle scale near the corner of the base plate to give accurate grid references for specific scales of map (eg 1:25,000, 1:50,000). Map scales, along the baseplate edge, measure distances, again for different scales of map.

» Compasses are affected by pylons, magnets, metal (check your camera kit and mobile phone) and magnetic rock, such as the Cuillins, on Skye.

» A compass is almost useless if you don t know how to use it properly. Mountain guides (as in, actual people), books, video tutorials and websites can teach you to use a compass. For a simple introduction (with pictures) try www.compassdude.com

RECTA Elite / DT420

Elite is a good example of a classic base-plate compass, and is ideal for fast and easy map work. It has a transparent base-plate, magnifier for seeing map details, romer scale for 1:50,000 and map scales for 1:25,000 and 1:15,000. The bezel (rotating compass housing) is chunky and easy to turn with gloves. Non-slip feet stop it skidding on the map.

 altimeter barometer

You can set the needle for declination via a tiny screw on the back of the compass, although you need a jeweller s screwdriver. Angle of slope can be measured (with the clinometer); useful in snowy mountains to help assess avalanche potential. Elite is easy to use and best for short distances, since the base-plate length only allows relatively short bearings to be accurately taken.

Burton McCall, www.burton-mccall.co.uk, 0116 234 4611

RECTA Officer / DP 6

Officer is part of Recta s DP range of sighting compasses. It has a box-like body with a small compass at one end and a mirror that slots into the housing when the compass capsule is laid on a map. The compass has horizontal and vertical grid lines so is easy to line up on a paper grid. The mirror drops out of the housing at the correct angle for reflective viewing of the compass face. Reading the bearing through the mirror while aligning the markers along the centre of compass and housing, is intuitive and provides a very accurate sighting line over distance. Declination can be set via a tiny screw on the compass; Recta even provide the tool, along with easy-to-follow instructions.

Burton McCall, www.burton-mccall.co.uk, 0116 234 4611

SILVA Ranger S

This sighting compass —base-plate with mirror —is intended for accurate, long-distance bearings. It works by reflecting the compass face in the mirror tilted at an angle of 45° from the base-plate (the correct angle is attained once the mirror cross-wire locates on the centre of the reflected compass face). A sighting hole allows accurate identification of distant objects. It s bulkier than a base-plate but easier to navigate with over rough terrain or in wide open spaces. Ranger S has map scales for 1:25,000 and 1:50,000, but no romer. Declination canbe fixed but there are inset declination scales. The bezel is rubberised, making it easy to turn with or without gloves. A standard base-plate version without the mirror is also available (Ranger, ?23).

Silva UK, www.silva.se, 01506 406277

SUUNTO Core

I find altimeter watches indispensable Among the best is this versatile Suunto Core incorporating watch, altimeter, barometer and compass among many other functions. Once the compass has been calibrated and declination set, arrows and numbers give direction and bearing.

It s tricky to take a bearing from a map as there is no base-plate but, because the watchouter ring rotates like a bezel, it can be set to point and lock on to a specified bearing. As a pure compass it s harder to use than a base-plate but is a great navigational back-up. Core s user manuals are clear and it s easy to switch between modes.

I navigate by combining altimeter and compass functions, and having them both on my wrist makes this a winner. I won t leave home without one. Suunto, www.suunto.com

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