Airspeed for best single-engine rate-of-climb  at gross weight and Sea Level  80  I00  I60  I20  I00  200  240 220  200 I80  I60  I40 I20  I00  80  60  40  KNOTS  Blue radial line  Green arc  White arc  Yellow arc  Red radial line  Figure 5-15.  Color codes for an ASI. field of another, the unlike poles attract each other and like  poles repel. Magnetic Compass Construction The float and card assembly has a hardened steel pivot in its  center that rides inside a special, spring-loaded, hard-glass  jewel cup. The buoyancy of the float takes most of the weight  off the pivot, and the fluid damps the oscillation of the float  and card. This jewel-and-pivot type mounting allows the float  freedom to rotate and tilt up to approximately 18° angle of  bank. At steeper bank angles, the compass indications are  erratic and unpredictable. An aircraft magnetic compass, such as the one in  Figure 5-16 ,  has two small magnets attached to a metal float sealed inside a  bowl of clear compass fluid similar to kerosene. A graduated  scale, called a card, is wrapped around the float and viewed  through a glass window with a lubber line across it. The card  is marked with letters representing the cardinal directions,  north, east, south, and west, and a number for each 30°  between these letters. The final “0” is omitted from these  directions; for example, 3 = 30°, 6 = 60°, and 33 = 330°.  There are long and short graduation marks between the letters  and numbers, with each long mark representing 10° and each  short mark representing 5°. The compass housing is entirely full of compass fluid. To  prevent damage or leakage when the fluid expands and  contracts with temperature changes, the rear of the compass  case is sealed with a flexible diaphragm, or with a metal  bellows in some compasses. The magnets align with the Earth’s magnetic field and the  pilot reads the direction on the scale opposite the lubber line.  Note that in  Figure 5-16 , the pilot sees the compass card from  its backside. When the pilot is flying north as the compass  shows, east is to the pilot’s right, but on the card “33”, which  represents 330° (west of north), is to the right of north. The  reason for this apparent backward graduation is that the card  remains stationary, and the compass housing and the pilot  turn around it, always viewing the card from its backside. Magnetic Compass Theory of Operations Figure 5-16. A magnetic compass. The vertical line is called the  lubber line. Figure 3-16. A Magnetic compass. Magnetic fields caused by aircraft electronics and wiring  can effect the accuracy of the magnetic compass. This  induced error is called compass deviation. Compensator  assemblies mounted on the compass allow aviation  5-11 N-S  E-W 