Distributions of the 3-mm (left column) and 1.3-mm band (right column) fluxes of 0923+392, 3C 111, and 3C 273. Please note the different axis scales and bin sizes. In order to minimize the impact of irregular sampling, we binned all lightcurves (compare Fig. 1) in time using N bins with sizes Δt. The parameters N, Δt, and the sizes of the flux bins ΔS_ν are given in the respective diagrams. Errorbars indicate binomial errors. Continuous grey lines indicate approximations to the data composed of individual Gaussians (dashed grey lines). In three cases (0923+392 at 1.3 mm, 3C 111 at 1.3 mm and 3 mm) we also indicate the best-fitting log-normal distributions (dotted black curves).