P A P E R III Category X : Installation and Compensation of Direct Reading Compass ___________________________________________________________ Knowledge of general principles of magnetism, magnetic materials and permanent magnets; polarity and strength of bar magnets, the earth as a magnet; the magnetic meridian and its relationship to the geographic meridian. Knowledge of the general principles of construction for typical Aircraft Direct reading compasses, including the magnet system, damping liquid, verge ring and markings, lubber line, grid wires, shock absorbing suspension and corrector box; the inspection necessary for the detection of common defects that may arise in use. Knowledge of the procedure and points to be observed during installation of the compass in aircraft. Knowledge of the precautions to be observed in the choice of site for, and the preparation of a "swinging base" checking the base by means of a landing compass. Knowledge of the compensation of compasses in the Aircraft, including the observation of deviations, the calculations and adjustments necessary for corrections for Co-efficient A, B and C, the procedure to be followed after then corrections are made and the preparation of deviation cards and graphs. Knowledge of the use of landing compass for checking the compasses in Aircraft.