@article{Graf,
  author    = {Johannes Graf},
  title     = {Die zweite Teilung der Stunde. Zur Geschichte der Sekunde},
  series = {PTB-Mitteilungen},
  volume    = {127.2017},
  number    = {3},
  issn      = {0030-834X},
  pages     = {5 -- 12},
  language  = {de}
}