Definition
Traditional mechanical Vertical Speed Indicators that display rate of climb or descent using a moving needle on a circular dial, typically calibrated in feet per minute. They sense changes in atmospheric pressure through a calibrated leak in a sealed instrument case and drive the needle proportionally to the rate of pressure change.
Plain English
The older style of climb-and-descent gauge — a round dial with a needle that swings up to show how fast you're climbing and down to show how fast you're descending.
Context Anchor
Seen when comparing traditional round cockpit instruments with the vertical speed tape on an electronic flight display.
Derivation
Analog' comes from the Greek analogos, meaning 'proportional.' An analog instrument shows a value by a continuously moving physical element (a needle) whose position is proportional to the quantity being measured — as opposed to a digital readout that shows discrete numbers.
Why Pilots Care
Many training aircraft and legacy fleets still use analog VSIs. Pilots transitioning between glass cockpits and traditional panels need to read both formats fluently. Analog needles give a quick visual sense of trend, which is why even modern PFDs often mimic the look with a moving tape and pointer.
Intuition Check
Analog does not mean inaccurate or outdated here. It means the information is shown by continuous needle movement on a dial rather than by a digital number or tape display.
Example Sentence 1
The Cessna 172 in the training fleet has analog VSIs, while the newer glass-panel aircraft display vertical speed as a tape on the PFD.
Example Sentence 2
Pilots flying older aircraft rely on analog VSIs to interpret vertical speed without needing a tape display.