The book covers many interesting applications, mainly in the field of electrical and radio engineering. All electrical formulas are written in the rationalized system of ISA units (in the international SI system). In the same system of units, numerical calculations are performed. When presenting numerical methods, the author limited himself mainly to techniques that can be performed using a manual counting machine and a set of tables. He does not consider special techniques related to the use of electronic computers, believing that this is within the competence of specialist programmers.