A-A-52024 Compass, Magnetic: Surveyor's And Transit, Pocket; With Optional Ball And Socket Joint Or Ball And Socket Head, And Jacob's StaffThis description covers two types of magnetic compasses, and includes the optional ball and socket joint, or ball and socket head, and Jacob's staff. Type I compasses are intend for use in topographical surveying field work done by the U.S. Forest Service. Type II compasses are used in geology and survey reconnaissance.

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A-A-52024

Index pointer. An index pointer shall be permanently secured to the inside wall of the compass box and shall extend over the compass dial. The index pointer shall be in line with the front sight and shall coincide with the north point for the compass.

Clinometer.  The clinometers shall consist of a tubular vial, a clinometers scale and a vernier index mounted on the compass box in such a manner that the clinometers may be rotated by an external leveler. The clinometers shall have its zero at the West cardinal point. Graduations shall extend on both sides of the zero and shall be in degree and percent declination. The degree scale shall be graduated every 1 degree, ±.50 degree, shall extend 90 degrees on each side of zero, and shall be numbered every 10 degrees. The vernier shall permit reading to 5 minutes. The percent scale extend 100 percent in both directions. Graduations shall be by 5 percent increments. Each 20 percent graduation shall be numbered.

Spirit level. A circular hermatically sealed spirit level shall be secured to the inside of the compass box in the Southeast or Northeast quadrant. The level shall not cover any essential inscriptions.

Dimensions and weights. The closed compass shall be not more than 4 by 4 inches, with rounded corners, by not more than 1.375 inches thick. The compass with carrying case shall weigh not more than 10 ounces.

Magnetic needle. The magnetic needle shall be between 2.000 and 2.250 inches long, with jeweled center and a stop.

Mirror and cover.  The mirror shall be bonded or otherwise mounted on a hinged cover attached to the south end of the compass box. The cover and the mirror shall provide a 0.375 by 0.4687 – inch clear glass window, an engraved center-line which will serve as an alternate front sight, and a folding front sight tip. Hinge friction shall be such as to permit setting of the mirror at any angle between full-closed and full-open position of the cover. Hinge stops shall be provided at 180 degrees open position. In the closed position, the cover shall actuate a lifting mechanism in the compass box to lift the magnetic needle from its pivot and hold the needle in place against the compass box window.

Cover latch. The cover shall latch into the closed position by use of a spring detent or closely controlled mechanical interference. The cover shall open by use of fingergrips (either natural or machined in) or by use of a push-to-open plunger-type spring release. When no mechanical opening aid is provided, fingergrips will be provided on the exterior of the cover and compass box.