Weight (defined as the GC expected number of good redshifts per deg²) of observed fields along a typical EWS progression (see Sect. 7). The moving median of the weights in the previous year is superimposed (red line, starting on year 1). The approximately regular cusps every 6 months are due to the paucity of observable fields close to the Galactic and ecliptic planes and their increased background and extinction. The decrease in the median and the upper envelope in the second half of the mission is due to a relatively low quality of the sky areas still available for observations in those periods. In fact, the best areas are observed in the first half of the mission (see Figs. 20 and 46).