Variations in the continuum flux at 5100 Å  (first panel), in the Hα and Hβ line fluxes (second and third panel, respectively), and in the integral Balmer decrement BD = F(Hα)/F(Hβ) (fourth panel) of the month-averaged profiles. The abscissa (OX) gives the modified Julian date (bottom) and the corresponding year (top). The continuum flux is in units 10^-15   erg   m^-2   s^-1   Å^-1 and line flux is in 10^-13   erg   m^-2   s^-1. The bottom panel gives the BD as a function of the continuum flux, where full circles denote the observations in Period I and open squares in Period II (see text).