@twinkinator: dual denominations are not only found on African coins. Think of the first British florins (1848-1887): the denomination there is "one florin - one tenth of a pound". Later they put "one florin - two shillings"(1893-1910). Other exemples of dual denominations are New Zealand "10 cents - shilling" 1967-1969 or in Danish West Indies "1/2 cent - 2 1/2 bit", "1 cent - 5 bit", "2 cents - 10 bit" and "5 cents - 25 bit"