The von Klitzing constant R K has been previously determined at the Bureau National de Métrologie (BNM) in 1986 and 1993. Considering the recommendation of the Comité Consultatif d'Electricité working group on the quantum Hall effect in 1988, as well as the differences between the values of the fine structure constant obtained from different methods, it appears to be particularly important that we continue to develop and improve the direct determinations of R K .

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