- Strictly speaking Roman Numerals never put more than three of any numeral together in a number. So you would count I, II, III, and then by placing a smaller numeral in front of a larger one, you would subtract; IV is 1 taken from 5, and so on.
- However, it's said that even in Roman times they didn't use IV for 4, because IV are the first two letters of the name of their king of the gods, Jupiter (IVPITER, as it was written).
- Today there are some clocks and sundials with 4 represented as IIII and some with IV. There are many suggested explanations why the 'incorrect' IIII is used in place of IV.
- This isn't just a clocks thing. Both methods of writing Roman numerals have been in use since the 1500s, possibly longer. Clock makers choose whichever number they feel is more aesthetically appealing and they often go with IIII because it balances better with VIII on the other side and makes the clock look more symmetrical. By the same token they use IX and not VIIII for 9 because it matches the III on the other side better.
- Louis XIV, king of France, who preferred IIII over IV, ordered his clockmakers to produce clocks with IIII and not IV, and thus it has remained.
- Using the standard numerals, two sets of figures would be similar and therefore confusable by children and others unused to reading clock faces: IV and the VI; and IX and XI. Since the first pair are additionally upside down on the face, an added level of confusion would be introduced. It is used to make greater character distinction between them by using IIII and VI.
- The four-character form IIII creates a visual symmetry with the VIII on the other side, which the two-character IV would not.
- With IIII, the number of symbols on the clock totals twenty Is, four Vs, and four Xs, so clock makers need only a single mold with a V, five Is, and an X in order to make the correct number of numerals for their clocks: VIIIIIX. This is cast four times for each clock and the twelve required numerals are separated:
- V IIII IX
- VI II IIX
- VII III X
- VIII I IX
- The IIX and one of the IXs are rotated 180° to form XI and XII. The alternative with IV uses seventeen Is, five Vs, and four Xs, requiring the clock maker to have several different molds.
- Only the I symbol would be seen in the first four hours of the clock, the V symbol would only appear in the next four hours, and the X symbol only in the last four hours. This would add to the clock's radial symmetry.