The variability analysis of PKS 2155-304
  In this paper, the post-1977 photometric observations of PKS 2155-304 are compiled and used to discuss the variation periodicity. Largest amplitude variations ($\Delta U = 1^{m}.5$; $\Delta B = 1^{m}.65$;   $\Delta V = 1^{m}.85 $; $\Delta R = 1^{m}.25$; $\Delta I = 1^{m}.14 $) and color indices ($(B-V) = 0.30\pm 0.06$; $(U-B) = -0.72\pm 0.08$;   $(B-R) = 0.62\pm 0.07$; $(V-R) = 0.32\pm 0.04$) are found.   The Jurkevich's method and DCF (Discrete Correlation Function) method indicate possible periods of 4.16-year and 7.0-year in the V light curve. 
J.H. Fan (CfA, Gnu, Cas-Pku.Bac) and R.G. Lin (CfA, Gnu)