Which of the following is not a gyroscopic instrument?

The speed indicator is not classified as a gyroscopic instrument because it functions based on the measurement of airspeed using differential pressure rather than relying on gyroscopic principles or mechanics. In contrast, gyroscopic instruments, such as the attitude indicator, turn coordinator, and heading indicator, utilize a spinning gyroscope to provide crucial information about the aircraft's orientation, angular motion, and heading.

The attitude indicator displays the aircraft's pitch and roll relative to the horizon using a gyroscope to maintain a stable reference point. The turn coordinator, similarly, employs a gyroscope to visually indicate the rate of turn, which aids pilots in maintaining standard rate turns. The heading indicator also relies on gyroscopic principles to show the aircraft's current heading, helping pilots navigate effectively.

In summary, the fundamental distinction lies in the operational principles of these instruments, making the speed indicator distinct in not being a gyroscopic instrument.