This instrument informs the pilot of the aircraft's rate of climb or descent. Like the altimeter, the VVI detects pressure changes to identify a climb or descent. However, unlike the altimeter, the VVI will calculate the rate of climb/descent and present this to the pilot in feet per minute (FPM).
A normal climb rate for a single engine general aviation aircraft is around 600 feet per minute. The backup VVI instrument (primary VVI can be displayed on the Heads Up Display) on the F-15E has a maximum rate of 6000 feet per minute. Since the Strike Eagle can easily exceed a climb rate of 20,000 feet per minute, this gauge is usually "pegged" at 6000 FPM.
