The purpose of the work is to study the addition of mutually perpendicular harmonic oscillations and the principle of operation of the electronic oscilloscope .. The content of the work consists in the observation of the trajectories of movements that are the result of the addition of mutually perpendicular harmonic oscillations of multiple frequencies, and in the determination of unknown frequencies by the Lissajous figure method .. Methodical instructions for laboratory work were developed at the Department of Physics of the Russian State University of Oil and Gas . and . M. Gubkina . Posted on the website of the Department of Physics http://physics. gubkin. ru.