Decimalisation is the process of converting a currency from its previous non-decimal denominations to a decimal system, i.e. a system based on one basic unit of currency and one or more sub-units, such that the number of sub-units in one basic unit is a power of 10, most commonly 100.Today, the only currencies which are in theory not decimal are the Malagasy ariary and the Mauritanian ouguiya, although in practice both of those are members of the large group of currencies with just one unit and no sub-unit.