Used by pilots and navigators to determine accurate true heading by the sun or stars in arctic regions. It is well suited for aligning a boat's compass while away from shore-based magnetic interference. It is also useful to celestial navigators and amateur astronomers for identifying stars. It also functions as a pelorus with extremely fast and simple operation. The astrocompass functions by means of measured movement in three independent axes. The uppermost member contains a peep sight for stellar use and a shadow bar for use with the sun. The main platform is adjustable by reference to two integral spirit levels. The MKII comes with complete instructions, carrying case and mounting base. These instruments were surplussed after World War II, and have been reconditioned. They are becoming quite rare, and their antique value is reflected in their price.