This compass has one folding sight; a slit in the lid serves as the second sight. Since the
lid is mirrored, the user can read the needle while sighting a distant object. The floating card is
graduated to degrees and numbered every ten degrees to 360. There is also a second (inner) row
of numbers in quadrants, reversed for reading in the mirror. This compass probably dates from the period 1890-1910. Keuffel & Esser donated it to the Smithsonian in 1972.
Ref: Keuffel & Esser, Catalogue (New York, 1906), p.427.