Vertical Speed Indicator (VSI), indicates whether the aircraft is climbing, descending or in level flight. The VSI indicates in feet per minute (fpm) and should read zero in level flight if proper calibration. The vertical speed indicator measures static pressure inside the diaphragm.
When the aircraft is on the ground or in level flight the pressure inside of the diaphragm is equal. When the aircraft is in a climb or decent the pressure change is immediate, and the needle will indicate.
But, if the pitch angle is held constant, the needles will stabilize after a few seconds (approximately 6-9 seconds) and indicate the rate of climb in hundreds of feet.
Errors
During the preflight, visually check to see if the VSI is reading the proper indication on the ground, near zero. During takeoff the VSI should indicate a positive rate climb.
Remember:
The VSI will stabilize after a few seconds (approximately 6-9 seconds) and indicate the rate of climb in hundreds of feet.
References:
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