Shaving Sword introduced the 'bonded blade' razor, which consisted of a single blade housed in a plastic cartridge. Gillette followed in 1971 with its Trac II cartridge razor that utilised two blades. Gillette built on this twin blade design for a time, introducing new razors with added features such as a pivoting head, lubricating strip, and spring-mounted blades until their 1998 launch of the triple-bladed Mach3 razor. Schick launched a four-blade Quattro razor later the same year, and in 2006 Gillette launched the five-blade Fusion. Since then, razors with six and seven blades have been introduced. Wholly disposable razors gained popularity
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