  Time variability of the photon flux is a known feature of active galactic
nuclei (AGN) and in particular of blazars. The high frequency peaked BL Lac
(HBL) object PKS 2155-304 is one of the brightest sources in the TeV band and
has been monitored regularly with different instruments and in particular with
the H.E.S.S. experiment above 200 GeV for more than 11 years. These data
together with the observations of other instruments and monitoring programs
like SMARTS (optical), Swift-XRT/RXTE/XMM-Newton (X-ray) and Fermi-LAT (100 MeV
< E < 300 GeV) are used to characterize the variability of this object in the
quiescent state over a wide energy range. Variability studies are made by
looking at the lognormality of the light curves and at the fractional root mean
square (rms) variability Fvar in several energy bands. Lognormality is found in
every energy range and the evolution of Fvar with the energy shows a similar
increase both in X-rays and in TeV bands.
