Visits A (upper two rows, brightness scale factor b = 50) and B (lowertwo rows, bightness scale factor b = 25), dither stations 1–2 from top to bottom, respectively. Left: observation (minimum stack of two images obtained at the same dither station, logarithmic brightness scale with range [-b, 100b]). The blue line marks the area that was included in calculating the sum of squared differences S. This area is off-centred in the direction opposite to the tail in order to avoid fitting the tailas best possible. Center left: best fitting model at the same brightness scale. Center right: difference between observation and model at a linear brightness scale, range [-10b, 10b]. Right: central seven pixels of observation with the sub-pixel positions of the two components marked. The brighter component is marked green, the fainter component is red. The brightness scale is linear in the range [-10, 100b]. The quantities f1 and f2 are the total counts from the two components in the simulation.