Regular measurements of solar radiation carried out in the network of actinometric stations of the former Soviet Union (FSU) have shown a decreasing tendency in the time series of direct and global solar radiation during last decades. A statistically significant decrease has been found in 60% of the time series of global radiation annual totals obtained from 160 actinometric stations. Three large areas, where this decrease exceeded 2% per 10 years, were found (in the European part of the FSU, in West Siberia, and in the Far East). As the main reason for changes in solar radiation, increased cloudiness and atmospheric turbidity are considered. A more detailed analysis of long-term changes in radiation budget components obtained from two stations situated in rather different conditions (Moscow Meteorological Observatory in a large town and Toravere Actinometric Station in a rural area) allows us to point out the influence of a large town as a source of air pollution on the radiation transfer in the atmosphere, as well as on cloudiness and air temperature.

An indirrect method is proposed for measuring small harmonic distortion factors, with a high accuracy. An analysis of methodological errors is given.

A microprocessor multimeter is proposed capable of carrying out a wide range of functions by means of software based on digital processing of the codes of the instantaneous values of the signals in accordance with certain algorithms. An estimate of its errors is given.