  In this review, I will discuss how to characterize synchrotron X-ray
variability of TeV blazars by using the observed/simulated light curves.
Apparently, temporal studies provide independent and complementary information
to the spectral studies, but surprisingly little attention has been paid
especially for the blazar study. Only exception is a classical argument for
presence of "time lag", which may (or may not) reflect the diffrence of
synchrotron cooling timescale. Also very recently, it was suggested that the
X-ray variability of TeV blazars indicates a strong red-noise, compared to a
fractal, flickering-noise of Seyfert galaxies. Various temporal techniques are
proposed in literature, e.g., the power spectrum density (PSD), the structure
function (SF), and the discrete correlation function (DCF) and other analysis
tools, but special care must be taken if the data are not well sampled and
observation is relatively short compared to a characteristic timescale of the
system. Also, the situation is being more complicated for low-Earth orbit
satellites, e.g., ASCA, RXTE and BeppoSAX, since the light curve inevitably
contains "periodic gap" due to the Earth occultation (every ~6ksec). I will
present detailed approaches to see how the "gap" and the "finite length" of the
data affects the results of temporal analysis, and to what extent we can
believe in our results. Finally, I will briefly comment on the high-sensitivity
X-ray observations with MAXI, that may shed new light on the forthcoming GLAST
era.
