There are six basic aircraft instruments pilots use during each flight in order to control the aircraft: the airspeed indicator, artificial horizon, altimeter, turn coordinator, direction indicator, and vertical speed indicator. The airspeed indicator (ASI) displays how quickly the aircraft is travelling. The majority of ASIs display speed in knots (kn). The colored bands around the display indicate safety information. The green band displays safe operating speeds while the white band specifies safe speeds to deploy wing flaps. The yellow band indicates the aircraft is operating at a higher speed than it is designed for and the red bar should be completely avoided.