Why on watches with Roman numerals write IIII, and not IV

Roman numerals were never used for calculations, but as a number system they were used to indicate numbers. Like most number systems of antiquity, Roman numbers were written according to the principle of addition, where I = 1, II = 2, III = 3, IIII = 4, V = 5, (...) VIIII = 9, (...) XVIIII = 19, ( ...) XXIIII = 24, we restrict ourselves to examples of numbers that will later be used on the clock to indicate 24 hours a day. During the imperial period, the principle of subtraction arose, where IV = IIII, IX = VIIII, XXIV = XXIIII, etc. With very few exceptions, this principle of deduction was not adopted for official instructions, monuments or sundials.

Clock (mechanism) measuring clock (unit of time) arose
at the end of the 13th century. When in the 15th century, manufacturers of watches gave this watch a dial, they chose Roman numerals, which by this time were already actively used in sundials. This tradition continued until 1582 and the introduction of the Gregorian calendar. From that moment, the watches on the dials ceased to be divided into 24 hours, but only into 12 sectors.



Why is IIII left?

- to visually balance VIII

- to form three groups of four numbers:

- from I: I, II, III, IIII

- from V: V, VI, VII, VIII

- from X: IX, X, XI, XII

- so that both sides of the vertical division of the dial were 14 digits.

An additional reason in favor of IIII is that on the radial dial, on which IIII, V, VI, VII and VIII are marked at an angle pointing down from the center, IV is difficult to read.

Notes:
1. translation with abbreviation (I did not translate about space).
2. It appears on the dial and uses both principles: addition - IIII and subtraction IX
3. On the Kremlin chimes and Big Bene (thanks tony ) - IV
4. As always, I will be grateful for additions, corrections and clarifications.