Why does this clock show 4 as IIII instead of IV?

"One common suggestion is that around the circle the IIII balances the VIII which is in its mirror-symmetrical place – that is if a mirror was placed vertically between the XII and VI, the VIII and IIII would reflect on to each other...

Another plausible explanation might be that IV has three strokes and is more likely than IIII to be confused with the neighbouring III or it could be confused with the upside down VI...

I think the answer is rather different. Artefacts in Wells Cathedral in Somerset, England indicate that it is the question that may be based on a false assumption. Have the normal rules of writing Roman numerals been broken? Or does the dial of a clock simply use the normal rules which were used when the clock face was first drawn in the 14th century? It is worth remembering that when the idea of a mechanism rotating hands to indicate the passage of time was invented, the means by which the pointers showed the time had to be designed.

The oldest surviving clock-face in its original condition is on the clock inside Wells Cathedral in Somerset. It dates from before 1392 and the original mechanism – now in the Science Museum – has some claim to be the oldest surviving clock works in the world. The current mechanism that drives it is Victorian, but the face has not been changed for more than 600 years...

The answer I believe is found in manuscripts in the Wells Cathedral library. They show that the use of IIII – or more precisely iiii or iiij – for 4 was commonplace even though 9 was normally depicted by IX or ix. In other words, the subtractive principle was used for one but not the other...

...in the mid 1200s, a copy of the Liber Ethinmologiarum by St. Isidore of Seville (died 636) was written out... The verso of folio 36 lists 39 headings. It uses iiii exclusively for 4, but ix exclusively for 9...

So the clock-faces we see today could be the last surviving remnants of the style used by the mediaeval scribes when writing Roman numerals."

Full credit for text and image to Paul Lewis.

From Roman numerals we move logically to Romania...