The formula E = mC2 is fundamental in Einsteinʼs special theory of relativity. It is given a new interpretation, where the operator C of transitions, which characterizes their speed, has a more complex mathematical structure and is controlled in contrast to a constant number, as is customary in relativistic mechanics. The possibility of using its proposed modifications related to the transition of mass to energy and energy to the mass of a physical body for solving engineering problems of classical mechanics, which is a special case of relativistic mechanics, is shown. As an example, the process of functioning of a machine which is a system of devices for converting energy and material, is considered. The efficiency of its functioning is evaluated through the operators of transitions of structural elements.
