Luopan

Abstract: Publisher Summary This chapter focuses on the various compass systems used in various countries. Dividing a circle into multiples of four and six equal parts is both very simple and a precise geometric construction, so most compass systems use one or both of them, along with halving an angle. Before 1920, compasses were marked with a variable-length abbreviation code based on the English names of the cardinal points, which gave 32 angular divisions around the circle. The Chinese use a compass called a luopan, which has a 24-part division, for feng shui, where each division on a luopan approximates a terrestrial day. The device is marked with several different rings with various purposes. Some European nations adopted the “grad” (also called “grade” or “gon”) system in the 19th century. It is similar to the metric system where a right angle has 100 grads, so a circle has 400 grads. These grads are then divided into tenths to get a circle of 4000 decigrads. The military adopted the French “millieme” system, which has the compass dial, divided into 6400 units, or “mils,” for additional precision. One mil subtends approximately one meter at a distance of one kilometer, which makes it useful for dropping artillery shells on people. The Qibla compass determines the direction of the Qiblah (Ka’bah) in Mecca and it is used by Muslims to determine the precise direction of Mecca for prayer.