This Stanley London® compass is a heavy solid brass reproduction of an antique stand surveying compass.
The side of the compass has an adjustable spirit level and the compass is mounted on a stand with three independently adjustable feet. The compass is free to rotate in azimuth on the stand. The inside of the lid has a mirror with a vertical line inscribed for use as both a rear sight, as well as to assist in reading the heading. A magnifying lens built into the front sight can also be used to read the compass heading. Closing the compass lid moves a needle lift mechanism that protects the jewel bearing when transporting the compass. The top of the lid contains a natural sine table and is labeled "Stanley London."
This compass measures 3 1/8 inches (7.9 cm) in diameter, stands 3 1/2 inches (8.9 cm) tall with the lid closed, and weighs 1 pound, 10 ounces (740 grams).
In practice, the spirit level is calibrated by setting the compass on a relatively level surface and adjusting the spirit level until the bubble reads the same distance from center when the compass is rotated 180-degrees on its stand. With the spirit level calibrated, the three threaded feet are adjusted so that the spirit level is centered for any azimuth. When an object is sighted through the sights, its magnetic heading can be determined from the main compass rose, and its heading with respect to true north can be read from the outer azimuth ring.