As Longstrider says: it has to do with aestetical balance. If you have a close look, you'll find 3 symmetrical groups, being:
- I, II, III & IIII
- V, VI, VII & VIII
- IX, X, XI & XII
Some people (want to) see the Holy Trinity (Father, Son, Holy Ghost / Spirit) in these 3 symmetrical groups.
Clocks weren't marked from the beginning of time
like this. Some makers of well known clocks used IV instead of IIII. Which makes it possible to place a specific clock in it's timeframe
or recognise it as a (bad) copy
(not everyone is aware of this difference, and simply copy the numbers from their IKEA clock
)
EDIT:
Neil, don't post when I'm having breakfast and at the same time try to answer on a thread mate