Compasses are used to find property lines, cruise plots,and lay out main skid trails and logging roads. This Suunto hand compass, with its mirror to see the red needle and its sighting notch, is accurate to about 2°. For greater accuracy a staff compass (a larger compass placed on a "Jacob's staff" thrust into the ground) or an engineer's transit or optical theodolite is used.
The second needle (the black one with arrowhead) is a pendulum so that the compass can be used on its side as a clinometer for measuring vertical angles. These angles, plus a little trigonometry, allow the calculations of tree heights and logging road grades.