Vertical Speed Indicator (VSI), also known as a Rate of Climb and Descent Indicator (RCDI) is an instrument which indicates the rate of climb or descent of an aircraft.

 

The VSI displays 2 different types of information 

: Direction of movement of the VSI needle where it shows an immediate indication of an increase or decrease in the aircraft's rate of climb or descent

: Rate information shows a stabilized rate of change in altitude