@article{Clette:3015,
      author        = "Clette, F. and Cliver, E. W. and Lefèvre, L. and
                       Svalgaard, L. and Vaquero, J. M. and Leibacher, J. W.",
      title         = "{Preface to Topical Issue: Recalibration of the Sunspot
                       Number}",
      year          = "2016",
      note          = "Topical Issue: Recalibration of the Sunspot Number",
}