Which instrument shows the aircraft's rate of climb or descent?

The Vertical Speed Indicator (VSI) is the instrument specifically designed to show the aircraft's rate of climb or descent. It measures the vertical speed in feet per minute (fpm) and provides real-time feedback to the pilot about how quickly the aircraft is ascending or descending. This information is crucial for maintaining altitude during flight, especially during climb and approach phases when precise control over altitude is necessary.

In contrast, the altimeter measures the aircraft's altitude above sea level, not the rate of climb or descent. The speed indicator provides information about the aircraft's airspeed, and the attitude indicator shows the orientation of the aircraft relative to the horizon, indicating whether it's climbing, descending, or turning. Each of these instruments serves a different purpose, making the VSI the appropriate choice for monitoring rate of climb or descent.