Just a heads-up for some upcoming events around the new SI: Everything is ready for the inauguration of the new Système International, the new SI, starting with World Metrology Day, 20th May 2019. https://www.bipm.org/en/measurement-units/rev-si/ NIST just announced a live celebration on November 2nd; https://www.youtube.com/watch?v=osU5o8pNgb0 and on their web site: https://www.nist.gov/si-redefinition The bipm, bureau international des poids et mésures, already hosts all draft documents for the new, exact definition of several constants of  nature, h, e, k, NA, which will in turn redefine the kg, the Kelvin and the Ampère, and also several derived units, like our beloved Volt and Ohm, which will get exact definitions inside SI, with zero uncertainty. https://www.bipm.org/utils/en/pdf/si-mep/MeP-a-2018.pdf From 13th to 16th November 2018, the CGPM, Conférence Générale des Poids et Mesures, https://www.bipm.org/en/cgpm-2018/ will meet in Versailles, to officially and ceremonially decide the new SI. The draft documents already contain the finalized values for the mentioned constants of nature, like h, e as derived from many experiments, ending July 1st 2017. These contain the defintion of the constants and units of the new SI: https://www.bipm.org/utils/en/pdf/CGPM/Convocation-2018.pdf The mise-en-pratique, or the practical realization also has been prepared, that are the cooking books, how to bring the units to real life. This process is of course not 'exact', as these described experiments inherently have some uncertainties. https://www.bipm.org/en/measurement-units/rev-si/#communication One effect will be, that the current Volt will cahnge by about 1E-7, and the Ohm by about 1E-9. There will be a live web cast, obviously during the final decision session, and with speeches about the quantum Hall effect, the Planck constant, optical atomic clocks, and about how the revised SI will work, including 2 Nobel laureates. Frank