Compass Types

There are a number of different types of compass designed for various uses:

• The first is the Air damped compass. This has a low accuracy and is what was commonly used in maritime before the development of stabilized compasses. They take a long time to settle so have very little use in modern navigation.

• Then there is the simple Map setting compass. They are the simplest and cheapest that you will come across. They have only basic measurements. You cannot set any variation on them so they take more thinking about.
• The common Silva-type mapping compass is the ideal map-reading compass. It has all the common scales. The magnetised needle is suspended in alcohol filled housing. This makes the needle settle a lot quicker. The housing has orienting lines for map work as well as detailed bearing lines etched on.

• The Prismatic Compass is a more expensive compass for more accurate navigation. This has a prism built in to allow the bearings to be read while sighting objects in the distance. It is quiet hard to understand and use so should really only be used by those that are experienced. The increased accuracy can be seen below.

• Electronic compasses also exist and are very expensive compared to others. They give accurate readings and have a number of snazzy features such as the ability to tell you if you are heading off course and store bearings in memory. Unfortunately, though, they suffer the same problems with nearby magnets and you may need a second compass to do any work on a map.

Compass Anatomy

Here is an animation to explain the different parts of the Silva-type compass, the most commonly used in Scouts:

• Scale Ruler - Used to measure distances on the map.
• Magnifier - To help read small details and view cluttered areas of symbols.
• Index Line - This is a line used to read off the bearing. Sometimes it is luminous.
• Direction of Travel Arrow - This points you in the direction you are going.
• Orienteering Lines - To help take bearings from a map.
• Parallel Lines - Lines parallel to the direction of travel arrow to help you take bearings on a map.
• Romer Scale - To help take grid references.
• Stencil Hole - For marking positions on the map.
• Baseplate - What everything is mounted on.
• Magnetic Needle - Points to magnetic north.
• Graduation Ring - Rotates with a degrees scale for giving bearings.
• Declination Scale - For adjusting for grid & magnetic north differences.