magnetic azimuth

Azimuth \Az"i*muth\, n. [OE. azimut, F. azimut, fr. Ar.
   as-sum?t, pl. of as-samt a way, or perh., a point of the
   horizon and a circle extending to it from the zenith, as
   being the Arabic article: cf. It. azzimutto, Pg. azimuth, and
   Ar. samt-al-r[=a]'s the vertex of the heaven. Cf. {Zenith}.]
   (Astron. & Geodesy)
      (a) The quadrant of an azimuth circle.
      (b) An arc of the horizon intercepted between the meridian
          of the place and a vertical circle passing through the
          center of any object; as, the azimuth of a star; the
          azimuth or bearing of a line surveying.
          [1913 Webster]

   Note: In trigonometrical surveying, it is customary to reckon
         the azimuth of a line from the south point of the
         horizon around by the west from 0[deg] to 360[deg].
         [1913 Webster]

   {Azimuth circle}, or {Vertical circle}, one of the great
      circles of the sphere intersecting each other in the
      zenith and nadir, and cutting the horizon at right angles.
      --Hutton.

   {Azimuth compass}, a compass resembling the mariner's
      compass, but having the card divided into degrees instead
      of rhumbs, and having vertical sights; used for taking the
      magnetic azimuth of a heavenly body, in order to find, by
      comparison with the true azimuth, the variation of the
      needle.

   {Azimuth dial}, a dial whose stile or gnomon is at right
      angles to the plane of the horizon. --Hutton.

   {Magnetic azimuth}, an arc of the horizon, intercepted
      between the vertical circle passing through any object and
      the magnetic meridian. This is found by observing the
      object with an azimuth compass.
      [1913 Webster]