The attitude indicator -- formerly known as the artificial horizon -- is a flight instrument that informs the pilot of the orientation of the aircraft relative to Earth's horizon. The miniature aircraft and horizon bar on the display mimic the relationship of the aircraft relative to the actual horizon and is a crucial aid for flying in poor weather conditions: it provides an immediate warning of the smallest change in orientation.

The components of the attitude-indicator display include a symbolic miniature aircraft, mounted so that it appears to be flying relative to the horizon. An adjustment knob, to account for the pilot's line of vision, moves the aircraft up and down to align it against the horizon bar. The top half of the instrument is blue to represent the sky, while the bottom half is brown to represent the ground. The bank index at the top shows the aircraft angle of bank. Reference lines in the middle indicate the degree of pitch, up or down, relative to the horizon.

At the heart of the attitude-indicator system is a gyroscope that spins at high speed: this is mounted so as to stay upright while the aircraft pitches and rolls. This mounting is achieved using a gimbal, a pivoted support that allows the rotation of an object about a single axis: the gimbal principle is illustrated in the picture.

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