BibTeX https://www.ptb.de/cms/nc/ptb/fachabteilungen/abt1/fb-17/liste-der-veroeffentlichungen/liste-der-veroeffentlichungen-der-arbeitsgruppe-171.html?tx_bib_pi1%5Bexport%5D=bibtex
It began in September 2011.}, web_url = {http://www.metrology-journal.org/10.1051