Compasses discussed in this chapter are devices used to determine direction, with a magnetized needle balanced on a pivot. The needle and pivot are housed in a box containing a circular ring divided into degrees and/or half-degrees. When a compass is held steady, and the needle swings freely, it points in a northerly-southerly direction, and the degree mark to which it points can be read on the circle.
KeywordsSecular Variation Magnetic Bearing Vertical Angle National Geophysical Data Center National Geodetic Survey
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