Mach number temperature generally decreases with increasing altitude between sea level and , the speed of sound also decreases. For example, the standard atmosphere model lapses temperature to at altitude, with a corresponding speed of sound (Mach1) of , 86.7% of the sea level value. While the terms "subsonic" and "supersonic", in the purest sense, refer to speeds below and above the local speed of sound respectively, aerodynamicists often use the same terms to talk about particular ranges of Mach values. This occurs because of the presence of a "transonic regime" around M = 1 where approximations of the Navier-Stokes equations used
Ford Mustang Mach 1 than six factory performance Mustang models were available (GT, Boss 302, Boss 429, Shelby GT350, Shelby GT500 and the Mach 1). Additionally, seven variations of V-8s were available in the '69–'70 models; most of these also available in the new Mach 1. Due to the Mach 1's success, the GT model was discontinued after 1969 following poor sales of 5,396 units versus the 72,458 sales for the Mach 1. The Mustang would not wear the "GT" badge again until 1982. The Mach 1 package was only available in the 'SportsRoof' body style (previously known as the 'Fastback'); never on the