The compass in its most fundamental form consists simply of a magnetic needle with a colored tip to indicate north, mounted on a pivot at the center of a compass card marked with the cardinal directions – N, S, E, W. Quadrants are normally subdivided, either by degrees or marked with lines to indicate NW, NE, SE, and SW. Wood-clad compasses are among the oldest designs, and pocket compasses one of the most common during the 18th and 19th Centuries. Pocket compasses are usually design like pocket watches with a hinged lid or a cover cap.

Sundials (dials) are known from at least 600 B.C. Egypt and China and 500 B.C. Greece. There are over a dozen different, formally designated types of sundials but they are typically circular, oblong or rectangular in shape, made of wood, ivory, silver or brass and marked to indicate time. All are fitted with a gnomon or vertical shadow-casting protrusion, which, on some types, is simply a thin string. They were sized to either mount on a table or pedestal or carry in the pocket. Some are constructed to be oriented with the disk horizontal, others vertical and still others inclined. Compasses were fitted to sundials during the late 1200s A.D. and a great number were made during the 1600s and 1700s. They were used to adjust clocks and pocket watches as well as to tell time themselves. They continued to be popular as pocket watch size instruments for calibrating watches until the mid-1800s when the widespread and accurate clocks of telegraph companies made sundials largely obsolete.The dipleidoscope, a sophisticated type of dial, was invented in 1843 by Edward Dent. By marking the meridian passage of the sun using a prism, compass and magnifying lens, the instrument determines time to within a few seconds of accuracy. The nocturnal is a related devise popularized in the early 1500s. It is used to find time at night with reference to the circumpolar stars. The nocturnal was used well into the 1700s and revived during the World Wars as a celluloid version called a ‘star clock’ as backup for military troops.

Terrestrial compasses used by surveyors and geologists are usually fit with two sighting alidades, hinged so they can be turned down against the compass face when not in use. These compasses are usually marked either from 0-360° azimuth or in quadrants from 0-90° with east and west reversed so the needle registers the direction of the pointer. The first recorded use of compasses in surveying was during the early 1500s when they were mounted first to astrolabes then circumferentors and graphometers. They remained a mainstay of surveying through the twentieth century. Geologic compasses are typically fitted with a vertical angle indicator needle fixed at the center of the compass card with the needle, so it rotates by gravity to indicate vertical angle when a flat side of the compass case is placed against an inclined plane.The prismatic compass was designed in 1812. It is a surveying compass that has a right angle magnifying prism attached to the back site with which to read fractions of a degree from the scale. Compasses have been made as wrist straps, mounted on walking cane handles and map chartometers, and made as watch swabs, brooches and pins.

Marching and traversing compasses are built on the same basic design as sighting and geologic compasses but without sighting alidades. Some have a normal compass needle, others a rotating compass card with a fixed azimuth dial around the periphery. Developed in the early 1900s, the compass case is commonly filled with fluid to dampen or slow down the otherwise erratic movement of the compass card that rests on a pivot with the magnetic needle attached either on top or bottom of the card. Compasses of this type are usually small and fitted with a hinged lid, sometimes with a ‘Hunter’ glass window.

Marine compasses are usually mounted in a protective housing like a wood box or a wood or brass dome called a binnacle. The first reference to gimbals on compasses for marine navigation was in 1537. The azimuth compass is a large marine compass used at sea to sight on the sun at sunup or at noon in order to determine magnetic deviation from true north. This application requires knowing the date and latitude, enabling the crew to calibrate the ship’s navigational compass to true north. The card of a mariner’s compass has 32 divisions called rhumb-lines instead of 360 degrees. Rhumb lines simplify navigational headings and tracking especially in high winds and rough waves.