The book of a physicist from Germany is devoted to the principles underlying the physical experiment. Systems of units, questions of experiment planning, laws of similarity of mechanics, optics of charged particles, plasma physics are considered. It is shown how it is possible to study processes in complex systems using models, the basics of error theory, features of various transmission devices, signal transmission problems, issues of natural measurement limits, charged particle and electromagnetic radiation detectors, as well as high-resolution spectroscopy methods are briefly described. For students, as well as engineers and scientists.