A Feng Shui Compass or 'Luopan Compass' is a model of the cosmos. The Feng Shui Compass consists of a central space 'Heaven's pool' that contains the magnetic needle which points south, a round inner plate with many rings with different Feng Shui meanings (including the energies within the Bagua) and an outer square plate with a spirit level, that may be pressed against a wall to determine the facing direction for a building.
There are different types of Luopan Compass used today, the one I use was designed by Howard Choy and made by Ricky Than in Hong Kong
