Distribution of the G magnitude of the source (top) and impact parameter (bottom) as well as the resulting relative standard error of the mass determination for the investigated events. The grey, red, yellow, and green parts correspond to a relative standard error better than 100%, 50%, 30%, and 15%, respectively. The thick black line shows the distribution of the input sample, where the numbers at the top show the number of events in the corresponding bins. The thin black line in the bottom panel shows the events during the nominal mission. We note the different bin width of 0.33″ below ϕ_min = 2″ and 1″ above ϕ_min = 2″ in the bottom panel.