Machmeter
![Illustration showing the face of a Machmeter reading a Mach number of 0.83](/Images/godic/202501/25/Machmeter.SVG2446.png")
A Machmeter is an aircraft pitot-static system flight instrument that shows the ratio of the true airspeed to the speed of sound, a dimensionless quantity called Mach number. This is shown on a Machmeter as a decimal fraction. An aircraft flying at the speed of sound is flying at a Mach number of one, expressed as Mach 1.