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 horsepower calculations. The following year also produced the fewest Mach 1 sales of the 1971-73 generation. There are no major differences in the '71 and '72 Mustangs externally, other than the addition of a "Mustang" script on the right side of the trunk panel (excluding Mach 1). The '72 Mach 1 also saw deletion of the pop-open gas cap, which was replaced with the standard twist-on cap found on the other Mustang models that year. The 302 Windsor remained as the base Mach 1 engine, with the 2 or 4 barrel 351 Clevelands as the only options. In 1973, the