Arithmetic in which the base of the notation is 2 instead of 10. The unit followed by a cipher signifies two, by another unit it signifies three, by two ciphers it signifies four, and so on. Thus, 10 signifies two, 100 signifies four; while 11 signifies 3, etc.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894
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