Spectral energy distributions for Mrk 501 in the three periods described in Sect. 3. The legend reports the correspondence between the instruments and the measured fluxes. Further details about the instruments are given in Sect. 2. The vertical error bars in the data points denote the 1σ statistical uncertainty. The black curve depicts the one-zone SSC model fit described in Sect. 6, with the resulting parameters reported in Table 2.