http://mathworld.wolfram.com/RomanNumerals.html

The following table gives the Latin letters used in Roman numerals and the ... not followed on the faces of clocks, where IIII is usually encountered instead of IV.

https://en.wikipedia.org/wiki/Roman_numerals

Roman numerals are a numeric system that originated in ancient Rome and remained the usual way of writing numbers throughout Europe well into the Late Middle Ages. Numbers in this system are represented by combinations of letters from the ... At some early time the Romans started to use the abbreviated forms IV ("one ...

https://www.dictionary.com/browse/roman--numerals

The Roman numerals for one to nine are: I, II, III, IV, V, VI, VII, VIII, IX. ... the first is subtracted from the second; thus, IV equals 4, XL equals 40, CM equals 900.

http://www.novaroma.org/via_romana/numbers.html

The Romans were active in trade and commerce, and from the time of ... After V comes a series of additions - VI means 6, VII means 7, VIII means 8. X, X means 10. But wait — what about 9? Same deal. IX means to subtract I from X, leaving 9.

https://monochrome-watches.com/why-do-clocks-and-watches-use-roman-numeral-iiii-instead-of-iv/

Aug 21, 2018 ... However, owners of watches with Roman numerals might have noticed ... While the numeral 4 is commonly written IV in the Roman numeric ...

https://www.infoplease.com/math-science/mathematics/numbers-formulas/roman-numerals

Roman numerals are expressed by letters of the alphabet and are rarely ... you can subtract 1 from 10 [IX] but not from 20—there is no such number as IXX).

https://www.rapidtables.com/math/symbols/roman-numerals/roman-numeral-4.html

The I roman numeral is equal to the number 1: I = 1. The V roman numeral is equal to the number 5: V = 5. Four is equal to five minus one: 4 = 5 - 1. IV is equal to ...

https://www.factmonster.com/math/numbers/roman-numerals

Several rules apply for subtracting amounts from Roman numerals: ... (that is, you can subtract 1 from 10 [IX] but not 1 from 20—there is no such number as IXX.).

https://www.britannica.com/topic/Roman-numeral

Apr 18, 2019 ... Quick Facts. clock with Roman numerals ... A symbol placed before one of greater value subtracts its value; e.g., IV = 4, XL = 40, and CD = 400.

https://www.rapidtables.com/math/symbols/roman-numerals-1-100.html

List of Roman numerals / numbers from 1 to 100. ... Number, Roman Numeral, Calculation. 0, not defined. 1, I, 1. 2, II, 1+1. 3, III, 1+1+1. 4, IV, 5-1. 5, V, 5.