What unit of measurement is used by the cabin vertical-velocity indicator to show the change in cabin altitude?

The cabin vertical-velocity indicator is specifically designed to measure the rate of change in cabin altitude, which is critical for monitoring the pressurization and decompression aspects of an aircraft's cabin environment. The unit of measurement used for this purpose is feet per minute. This measurement indicates how quickly the cabin altitude is rising or descending, allowing the flight engineer and crew to manage the pressurization system effectively.

When the cabin is climbing or descending, the vertical-velocity indicator reflects how many feet the altitude changes per minute, helping the crew assess the comfort and safety of passengers during flight. This rate is crucial, especially during ascent and descent phases, to ensure a smooth transition and to prevent potential physiological issues related to rapid changes in cabin pressure.

Other units such as pounds per square inch, cubic feet per minute, and inches of mercury relate to pressure measurements and airflow rather than the specific rate of cabin altitude change, making them unsuitable for this particular indicator.