The paper presents the results of a technique developed for OES measurements of plasma local parameters of electric arcs and jets, when they are non-stationary and can not be
accounted for using a common approximation of the axial symmetry. The technique uses physical "a priory" data, and it is based upon a plane symmetry approach to the plasmas under consideration. Rather simple equations are derived allowing to analyze the influence of the plasma temperature fluctuations on the measured intensities of spectral lines emitted by the arc/jet plasmas and thus on temperature measurement results. Some important conclusions are
made concerning the relations between measured intensities, local plasma temperature values and the temperature fluctuations. Among them, a technique is proposed to measure at a time maximum temperature along a line of sight and its dispersion value using an intensity ratio of three atomic spectral lines, emitted by unstable arcs/jets, when fluctuations of the plasma parameters are stochastic ones. For the case of sinusoidal pulsations of the plasma parameters, it is found that a ratio of the measured mean intensity values of spectral lines gives the plasma
maximum temperature along the line of sight during the observation time.