Targets of WEBT campaigns have been, besides BL Lacertae, AO 0235+16 (Raiteri et al. 2001), Mkn 421, S5 0716+71 (Villata et al. 2000), Mkn 501, 3C 66A.

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Literature data have been taken from Maesano et al. (1997), Fan et al. (1998; with dates taken from Fan & Lin 2000), Webb et al. (1998), Bai et al. (1999), Tosti et al. (1999), Ghosh et al. (2000), Katajainen et al. (2000), Clements & Carini (2001), Fan et al. (2001),Sobrito et al. (2001), Papadakis et al. (2003), Tosti et al. (2004). Sometimes the data used in this paper do not exactly correspond to the original ones since some correction/removal (often done in agreement with the data owners) was needed. Moreover, some datasets were completely re-analysed.

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