@misc{indiciae610c95026e3d,
  title = {Group Sunspot Numbers: Sunspot Cycle Characteristics},
  author = {Hathaway, D. H. and Wilson, R. M. and Reichmann, E. J. and Six, N. Frank},
  year = {2002},
  url = {https://ntrs.nasa.gov/citations/20020048587},
  note = {Source identifier: 20020048587}
}