Through this paper, we will get to know the basic physics principles on which the operation of devices for ultrasound diagnostics in medicine are based. Basic concepts such as definition of wave and sound wave, and the properties of a sound wave as a mechanical wave are defined. The importance of ultrasound in diagnostics lies in the fact that so far no harmful effects have been proven within the limits to which commercial devices are calibrated and irradiate the human body. In order to understand how ultrasound can be harmful, it is important to show how the ultrasound wave propagates throughout the body, which was done in this paper. The resolution of the device was analyzed and how errors in device settings can affect the quality of measurements. In addition to the working principle, three types of displays that can be seen on device's monitors have also been elaborated. The conclusion on the safety of application is based on data from literature, which are either textbooks for medical students or scientific articles related to radiology.