Second, when on a northerly heading and a turn towards the east or west is made, the magnet causes the compass to lag behind the actual heading the aircraft is flying through. This lag will slowly diminish as the aircraft approaches either east or west and will be approximately correct when on an east or west heading. When the aircraft turns further towards South, the magnetic compass needle will tend to lead the actual heading of the aircraft. When a turn is made from south to an east or west heading the compass will lead the actual heading the aircraft is flying through, it will diminish as the aircraft approaches either east or west, and it will lag as the aircraft turns further towards North. This happens in a coordinated turn because of the bank of the aircraft and resulting bank of the compass. The North-seeking pole of the magnet is pulled towards the earth's magnetic field in the turn. This results in an angular displacement of the compass. The magnitude of the lead/lag will be approximately equal to the aircraft's latitude. (An aircraft at 30° north latitude will need to undershoot 30° while turning directly north, and overshoot 30° while turning directly south) The pilot community uses acronym UNOS (undershoot North overshoot South) to memorize this rule. Some other acronyms which pilots find easier to remember is NOSE (North Opposite, South Exceeds), OSUN (Overshoot South, Undershoot North), and South Leads, North Lags in the southern hemisphere This guideline is based not on a standard-rate turn, but on a bank angle of 15°-18°, which would equal a standard rate turn at the airspeeds typical of light aircraft.