BVR photometry of comparison stars in selected blazar fields - II. Photometric sequences for 9 quasarsC. M. Raiteri, M. Villata, L. Lanteri, M. Cavallone and G. SobritoAstron. Astrophys. Suppl. Ser., 130 3 (1998) 495-500DOI: https://doi.org/10.1051/aas:1998420