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Ciuryło and M. Zawada, Nature Astronomy 1, 0009 (2016) https://doi.org/10.1038/s41550-016-0009 Absolute frequency measurement of the 1S0 – 3P0 transition of 171Yb M. Pizzocaro, P. Thoumany, B. Rauf, F. Bregolin, G. Milani, C. Clivati, G. A. Costanzo, F. Levi and D. Calonico, Metrologia 54, 102 (2017) https://doi.org/10.1088/1681-7575/aa4e62 Funding statement: Support has been received from the project EMPIR 15SIB03 OC18. This project has received funding from the EMPIR programme co-financed by the Participating States and from the European Union’s Horizon 2020 research and innovation programme. Publicity resources – repository instructions and EURAMET logos