What is vario meter?

Vario meter, also known as a rate of climb indicator, is an instrument used in aviation to measure the rate of ascent or descent of an aircraft in feet per minute (ft/min). It works by measuring the difference in air pressure between the static pressure port and the ram air pressure port. When the aircraft is climbing, the pressure at the ram air pressure port increases and causes the diaphragm inside the vario meter to expand, which in turn creates a movement in the attached needle, providing an indication of the rate of climb. Conversely, during a descent, the diaphragm compresses, causing the needle to move in the opposite direction indicating the rate of descent. Vario meters are commonly found in gliders and sailplanes, where they are used to locate and stay in rising columns of air (thermals) to extend the duration of flights.