Once the static as well as ram pressures are equalized, the columns attain the same height on the Air Speed Indicator. The mercury on the ram part of the tube pushes back once the ram pressure rises. The Turbine Speed also makes the columns imbalanced once the tube is pushed back. The mean between the columns can be marked for indicating the speed of the aircraft. This is a value that is known as the indicated air speed and may be observed in the knots, or other units like miles per hour.

As the Air Speed Indicator is marked at a standard pressure and pressure, the readings are often inaccurate as well as different during different temperatures and altitudes. An incorrect indicated air speed is used for determining the tendency of an air craft to stall. Electronically accurate instruments for determining differences in Altitude and temperature help in determining the position of the aircraft.

A faster Air Speed Indicator helps in measuring the accurate air speed that is relative to the sound. This Indicator is known as a Mach meter.