epoch-folding technique are more conveniently presented by plotting the inverse period (frequency) along the x-axis and by specifying a linear frequency grid in the calculations. In this case, the absolute FWHM of the peaks corresponding to periodicities with similar shapes is the same in the frequency spectrum at any periods. If we plot the parameter ${\sigma^2} \over T$ ($T$ is the period in bins) along the $y$ axis, the frequency continua of noise components correspond, to an accuracy of a factor, to those of a power spectrum in a Fourier analysis. In particular, the quantities that characterize shot noise are constant at all frequencies (white noise). The scatter of points in the real spectrum about the frequency-averaged values of ${\sigma^2} \over T$ in the noise segments in the vicinity of the peak under consideration gives the variance $\sigma_{\sigma}$, which can be used to estimate the significance of the periodicity corresponding to this peak (in the case of Prognoz 9 data $\sigma_{\sigma}$, values were calculated with the use of $\pm50\cdot\Delta T_{FWHM}$ relative to the peak, where $\Delta T_{FWHM}$ is the mean width of the peak on the periodogram; for these intervals, the background level between peaks was essentially constant). Since the 