Which instrument provides crucial information about the aircraft's vertical speed?

The vertical speed indicator is an essential instrument in an aircraft that specifically measures and displays the rate of climb or descent. It indicates whether the aircraft is ascending or descending, and at what rate, typically in feet per minute. This information is vital for pilots to maintain desired altitude during climb, cruise, and descent phases of flight, helping them to avoid altitude loss during approaches or ensure a safe ascent rate.

The other instruments serve different functions; for example, an artificial horizon indicates the aircraft's orientation relative to the horizon, which is essential for maintaining level flight or during turns. The magnetic compass shows the aircraft's heading, helping with navigation but not with altitude-related metrics. The altimeter measures the aircraft's altitude above sea level but does not indicate the rate of climb or descent, making the vertical speed indicator the go-to instrument for vertical speed information.