section_path: Description/Other forms/Other subtractive forms
section_name: Other subtractive forms
paragraph_text: Other subtractive forms
  
  There are numerous historical examples of IIX being used for 8; for example, XIIX was used by officers of the XVIII Roman Legion to write their number. The notation appears prominently on the cenotaph of their senior centurion Marcus Caelius (c. 45 BC – 9 AD). On the publicly displayed official Roman calendars known as Fasti, XIIX is used for the 18 days to the next Kalends, and XXIIX for the 28 days in February. The latter can be seen on the sole extant pre-Julian calendar, the Fasti Antiates Maiores. There are historical examples of other subtractive forms: IIIXX for 17, IIXX for 18, IIIC for 97, IIC for 98, and IC for 99. A possible explanation is that the word for 18 in Latin is duodeviginti — literally "two from twenty" — while 98 is duodecentum (two from hundred) and 99 is undecentum (one from hundred). However, the explanation does not seem to apply to IIIXX and IIIC, since the Latin words for 17 and 97 were septendecim (seven ten) and nonaginta septem (ninety seven), respectively.
  
  The ROMAN() function in Microsoft Excel supports multiple subtraction modes depending on the " Form " setting. For example, the number "499" (usually CDXCIX) can be rendered as LDVLIV, XDIX, VDIV or ID. The relevant Microsoft help page offers no explanation for this function other than to describe its output as "more concise".