When Roman numerals are used on a clock face, why is the number 4 usually written as IIII rather than IV? Are there any other instances where IIII is used in favour of IV?

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When Roman numerals are used on a clock face, why is the number 4 usually written as IIII rather than IV? Are there any other instances where IIII is used in favour of IV?

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Someone once told me it was to differentiate between 4 and 6, but that has never made any sense to me

IIII and VIIII were the original forms of 4 and 9; IV and IX came into use a bit later but there really wasn’t ever a standardized style like you’d think there would be. Some clocks have IV and some have IIII and it may just come down to stylistic preference or the lineage of the clockmaker.

Ok, IIII is sometimes used on a variety clock or watches – it has nothing to do with quality, it is more of a “watchmaking tradition/quirk”. Correct way is to write IV as 4, but it was not always so – the oldest version of roman numbers used IIII as 4 and VIIII as 9. So it can be found in some historical instances. Now why only watchmakers decided to keep 4 as IIII instead of newer, more common IV is a point of many discussions and theories, but simply put – we don’t know for sure! There are theories, that it was because ancient roman pocket sundials (yes, they were a thing) did not want to feature IV, since it would seem as a reference to IVPPITER (god Jupiter) and it would be blasphemous, so they used the “older” writing IIII. Some theories are also about “it is easier to read upside down”, but hey you have IX as 9 and XI as 11, so that is wonky theory. Then there is a theory that it was to save up money, because you could use mold for “I” 4 times instead of 3, which also seems shady. And of course theory “it is easier to understand for uneducated masses in 18-19th century” (why then you don’t write 9 as VIIII?!). So it remains a mystery and bit of an unusual trivia in the history of clock making.

TL;DR: It was an older way to write 4 for romans. We don’t really know why is it traditional on clocks.

Decades ago, on a visit to Fort York in Toronto, one of the docents pointed out a large clock in the officers mess which had IIII instead of IV. Their explanation was that George IV (King of the United Kingdom 1820 – 1830 ) preferred to keep IV for the royal title, so clocks were required to use IIII instead. No idea how true this is, but it’s a good story.

In addition to clocks, there is at least one more use: precision class of commercial scales. There are classes from I (very high precision) to IIII (very rough, higher deviations allowed).

Source: NIST Handbook 44 (unfortunately, not really public as you have to buy it from NIST).