Geology

Brunton compasses have three main parts, box, sighting arm, and lid. The box contains most of the components: the needle; bull's eye level (round level to read horizontal angles); clinometer level (barrel-shaped) and clinometer scale (for reading vertical angles); damping mechanism (to more efficiently stabilizing the needle); lift pin (to lock the needle); side brass screw and index pin (to set and display the declination); graduated circle or card (to read the bearing). The needle has two ends: the north-seeking end (commonly white in genuine Brunton compasses, labeled 'N' in others), and the black, south-seeking end. The north-seeking end of the needle is pulled down in the northern hemisphere where the magnetic inclination is downward. An additional small weight attached to the south-seeking end of the needle provides proper balancing of the needle. The weight needs to be reversed if using the compass in the southern hemisphere where the magnetic inclination is upward.

The lid, attached to the box with a hinge, contains the mirror with the axial line and oval sighting window (for waist- and eye-level sighting), and the sight. The long sighting arm, attached to the box with a hinge, has a long, oval rectangular cutout or slot (for reading linear objects), and a tiltable sighting tip, which is used for aligning the line of sight. The circle card of the Brunton compass is designed in two traditional scales. The azimuth scale uses three digits, with north at 000o or 360o, and south at 180o. The quadrant scale uses an alphanumeric notation (e.g., N60oE, S20oW) with the card graduated in four 90o quadrants (NE, SE, SW, NW); north and south lie at the two upper and lower 0o marks, respectively.