Top: distribution of the average durations of the microlensing magnification episodes obtained from the simulations for Σ = 0.5 and v = 300 km s^-1. Horizontal shaded region depicts the range 60−120 days of the apparent variability time scales of the magnification factor ratio in B0218+357, and the vertical one depicts the microlensing magnification ratio range, suggested by the observations. Bottom: cumulative probability of observing microlensing magnification factor ratio >μ for different source sizes, estimated from the simulations. The vertical shaded region is the same as in the upper panel.