Atomic Weights and the International Committee —A Historical Review Chemistry internaional Vol. 26 No. 1 January February 2024 -
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In April 1957 at the bar in the Hotel Krasnapolski in Amsterdam, Nier suggested to Mattauch that the 12C=12 mass scale be adopted because of carbon's use as a secondary standard in mass spectrometry. Also, 12C = 12 implied acceptable relative changes in the atomic weight scale, i.e., 42 parts-per-million (ppm) compared to 275 ppm for the 16O = 16 scale (which would not acceptable to chemists)."
