A Turn Coordinator utilizes a gyroscope mounted at a 30° angle to the longitudinal axis of the airplane, which makes it sensitive to turning as well as rolling. A miniature airplane with wings that pivot shows the direction of bank. Aligning the wingtips with the calibrated hash marks indicates a standard-rate turn. The instrument also has an inclinometer consisting of a black glass ball sealed inside a curved black tube that is partially filled with liquid. The ball measures the relative strength of the force of gravity and the force of inertia caused by a turn. The miniature aircraft in the turn coordinator displays the rate of turn, rate of roll and direction of turn. The ball in the tube indicates the quality of turn (slip or skid). In a SLIP the ball is on the inside of the turn—the rate of turn is too slow for the amount of bank. In a SKID the ball is on the outside of the turn—the rate of turn is too fast for the amount of bank. Typically, the turn coordinator is electrically powered, but can also be powered by air. In the event the Attitude Indicator fails, the Turn Coordinator can be used as a backup to keep the wings level.