Razor to shave themselves more, the demand for barbers providing straight razor shaves decreased. In 1960, stainless steel blades which could be used more than once became available, reducing the cost of safety-razor shaving. The first such blades were made by the Wilkinson firm, famous maker of ceremonial swords, in Sheffield. Soon Gillette, Schick, and other manufacturers were making stainless-steel blades. These were followed by multiple-blade cartridges and disposable razors. For each type of replaceable blade, there is generally a disposable razor. In the 1930s, electric razors became available. These can rival the cost of a good straight razor, although the
Mach reflection the shock angle exceeds a certain value, the deflection achievable by a single reflected shock is insufficient to turn the flow back to a direction parallel to the wall and transition to Mach reflection is observed. Mach reflection consists of three shocks, namely the incident shock, the reflected shock and a Mach stem, as well as a slip plane. The point where the three shocks meet is known as the 'triple point' in two dimensions, or a shock-shock in three dimensions. The only type of Mach reflection possible in steady flow is direct-Mach reflection, in which the Mach stem is