Left panel: Flux distribution from ∼12 years of R-band observations. The histogram (blue bars) shows the flux counts. The red curve is the best-fitting normal function, and the blue curve is the best-fitting log-normal function. Right panel: RMS (i.e., the square root of the excess variance) as a function of the mean flux, computed in (1) bins containing an equal number of data points (blue markers), and (2) bins of fixed time length (red markers). The solid blue and red lines indicate the best linear fits for each binning scheme.