In old physics and engineering publications from the 1950s or so, it's common to see non-SI "double prefixes", such as a "millimicrosecond pulse", or a "10 micromicrofarad" capacitor.

These units are considered obsolete today. However, I failed to find a historical review on the use of these units.

  • In which year did units like "nano-" and "pico-" become parts the SI-standard?

  • When did the use of standard SI-prefix become common and largely replaced the "double prefixes" in engineering?


1 Answer 1


Resolution 12 of the 11th Conférence Générale des Poids et Mesures (CGPM) adopted 12 SI prefixes in 1960, including pico- and nano-. Google Ngrams show steep decline in the use of millimicro- after 1964, and micromicro- after 1966. Some other double prefixes, like kilomega- and hectokilo- were also in use, decimilli- was even standardized in Frace until 1961.


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