The Vertical Speed Indicator (VSI)
What is a VSI ?
This is vertical speed indicator from a typical light helicopter, in this case the Hughes / Schweizer 300.
It displays rate of climb or descent by moving a needle around the instrument face.
The needle is deflected upwards (clockwise) to indicate a climb, and downwards (anticlockwise) to indicate a descent.
The numbers around the scale are hundreds of feet per minute, and each graduation on the scale is one hundred feet per minute.
How does it work ?