General principles of digital measuring instruments construction are considered. As an example, the design of a digital measuring complex is given, with which it is possible to measure DC and AC voltages with sufficiently high accuracy, frequency. The complex has a built-in generator of low-frequency signals with low frequency response unevenness and a coefficient of nonlinear distortions, as well as a meter of nonlinear distortions. All measured values are displayed on a common digital display indicator. For trained amateur radio operators.