 On the publicly displayed official Roman calendars known as Fasti, the numbers 18 and 28 could be represented by XIIX and XXIIX respectively; the XIIX for 18 days to the next Kalends, and XXIIX for the number of days in February.The latter can be seen on the sole extant pre-Julian calendar, the Fasti Antiates Maiores.While irregular subtractive and additive notation has been used at least occasionally throughout history, some Roman numerals have been observed in documents and inscriptions that do not fit either system.