Roman fractions were based on a duodecimal system. From to they were expressed as multiples of twelfths ("uncia" "twelfth"; the source of the English words "inch" and "ounce") and from to they were expressed as multiple twelfths less than the next whole unit—i.e. a whole unit less , or respectively. There were also special terms for quarter ("quadrans"), half ("semis"), and three-quarters ("dodrans"). "Dodrans" is a Latin contraction of "de-quadrans" which means "a whole unit less a quarter" ("de" means "from"; "quadrans" means "quarter"). Thus for the example of 175 years, the term is a quarter century less than the next whole (bi)century or 175 = (−25 + 200).