Diptych Luopan (mariner's box compass), wood / metal / glass, maker unknown, retailed by Fang Xiushui's shop, Wan'an, Anhui Province, China, mid 19th century - early 20th century.
Luopan is a Chinese magnetic compass, also known as mariner's compass or Feng Shui compass. It is used by mariners during navigations and also used by Feng Shui consultant to determine the precise direction of a structure or other item.
Like a conventional compass, a luopan is a direction finder. However, a luopan differs from a compass in several important ways. The most obvious difference is the Feng Shui formulas embedded in from 1 up to 40 concentric rings on the surface. This is a metal or wooden plate known as the heaven dial. The circular metal or wooden plate typically sits on a wooden base known as the earth plate. The heaven dial rotates freely on the earth plate.
A red wire or thread that crosses the earth plate and heaven dial at 90-degree angles is the Heaven Center Cross Line, or Red Cross Grid Line. This line is used to find the direction and note position on the rings. The schematic of earth plate, heaven plate, and grid lines is part of the two cords and four hooks geometrical diagram in use since at least the Warring States period.
A conventional compass has markings for four or eight directions, while a luopan typically contains markings for 24 directions. This translates to 15 degrees per direction. Interestingly, the Sun takes approximately 15.2 days to traverse a point. If you mark a series of 24 points on the ecliptic it creates a cycle of 365.25 days, which means that each degree on a luopan approximates a terrestrial day.
A luopan does not point to the north pole of Earth. The needle of a luopan points to the south magnetic pole (it does not point to the geographic pole). The Chinese word compass translates to "pointing-south needle".