ADAM HART-DAVIS / SCIENCE PHOTO LIBRARY ADAM HART-DAVIS / SCIENCE PHOTO LIBRARY
Compass. A modern Silva-type compass for use in conjunction with a map for finding directions. It is seen resting on an Ordnance Survey map. The Silva compass consists of a fluid-damped, magnetised needle fixed to a plastic ruler base. The north-seeking pole is indicated, with degrees west, south and east, and the needle is free to rotate on a pivot. The needle becomes aligned to the local component of the Earth's magnetic field, resting north to south. From this true north can then be calculated, and orientated to points on the map.
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