turning, but periodically check it in straight and level unaccelerated flight. Compass errors Several types of error will affect the heading indication provided by a magnetic compass if the aircraft is not in steady straight and level unaccelerated flight. Pitch limits A limitation imposed by a compass' construction is that the balancing bowl's pin, which is connected to a pivot point, only allows, in most compasses, the bowl to tilt by approximately 18 degrees before it will touch the side of the casing. When this happens its freedom to rotate is lost and the compass becomes unreliable. Magnetic dip A second limitation is magnetic dip. The compass dial will tend to align itself with the geomagnetic field and dip toward the northern magnetic pole when in the northern hemisphere, or toward the southern magnetic pole when in the southern hemisphere. At the equator this error is negligible. As an aircraft flies closer to either pole the dipping error becomes more prevalent to the point that the compass can become unreliable because its pivot point has surpassed its 18 degrees of tilt. Magnetic dip is caused by the downward pull of the magnetic poles and is greatest near the poles themselves. To help negate the effect of this downwards force, the center of gravity of the compass bowl hangs below the pivot. Compass navigation near the polar regions, however, is nearly impossible due to the errors caused by this effect. When in steady straight and level flight the effect of magnetic dip is of no concern. However, when the aircraft is accelerated or turned to a new heading the following two rules apply: First, when on an easterly or westerly heading and the aircraft accelerates, the center of gravity of the bowl lags behind the pivot, making it tilt forwards. Because of magnetic dip the compass will show a false turn towards the north if in the northern hemisphere or vice versa a false turn towards the south if in the southern hemisphere. Also if the aircraft is decelerated the compass will show a false turn towards the south in the northern hemisphere and false turn towards the north in the southern hemisphere. The error is neutralized when the aircraft has reached its velocity and the magnetic compass will then read the proper heading. Pilots in the northern hemisphere remember this by the mnemonic ANDS: accelerate north, decelerate south. The opposite