However, this is far from universal: for example, the clock on the Palace of Westminster tower (commonly known as Big Ben) uses a subtractive for 4 o'clock. Isaac Asimov once mentioned an "interesting theory" that Romans avoided using because it was the initial letters of , the Latin spelling of Jupiter, and might have seemed impious. He did not say whose theory it was. Several monumental inscriptions created in the early 20th century use variant forms for "1900" (usually written ). These vary from for 1910 as seen on Admiralty Arch, London, to the more unusual, if not unique for 1903, on the north entrance to the Saint Louis Art Museum. Especially on tombstones and other funerary inscriptions 5 and 50 have been occasionally written and instead of and , and there are instances such as and rather than or . Other subtractive forms There is a common belief that any smaller digit placed to the left of a larger digit is subtracted from the total, and that by clever choices a long Roman numeral can be "compressed". The best known example of this is the function in Microsoft Excel, which can render "499" (usually ) into , , or depending on the "" setting. There is no indication this is anything other than an invention by the programmer, and the universal-subtraction belief may be a result of modern users trying to rationalize the syntax of Roman numerals. There is, however, some historic use of subtractive notation other than that described in the above "standard": in particular for 17, for 18, for 97, for 98, and for 99. A possible explanation is that the word for 18 in Latin is , literally "two from twenty", 98 is (two from hundred), and 99 is (one from hundred). However, the explanation does not seem to apply to and , since the Latin words for 17 and 97 were (seven ten) and (ninety seven), respectively. There are multiple examples of being used for 8. There does not seem to be a linguistic explanation for this use, although it is one stroke shorter than . 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 ( – 9 AD). On the publicly displayed official Roman calendars known as Fasti, is used for the 18 days to the next