## Guide for this category...

Before the popularization of Arabic numerals, which are now a global standard, various other means existed of expressing numerical concepts. This section will provide a terse and dirty guide to the Roman method, which is used in niche areas today.

The chief fundamental difference between the Arabic and Roman systems is that the latter lacks a zero. In practice, this absence means that the number of digits is less important than the combination of the symbols. In the Arabic system, you can know 1000 is worth somewhat more than 978 because of the number of digits (and lack of a decimal point), but to someone uninitiated in Roman numerals, CMLXXVIII may well look more impressive than M.

There are fewer Roman numerals than Arabic ones, and some numbers are made by repeating certain symbols. A symbol will never be repeated more than three times in a row. Instead, larger numbers are modified by prefixing a single numeral, the next-highest one that represents a decimal number beginning with 1. In this case, the larger number is subtracted by the smaller one. Examples of this will be provided shortly.

Here's a table of Roman numeral values; examples of numbers will be shown below.

- M - 1000
- D - 500
- C - 100
- L - 50
- X - 10
- V - 5
- I - 1

Some examples of valid numbers:

I = 1

III = 3

IV = 4

IX = 9

XXXIX = 39

XL = 40

XC = 90

CD = 400

CM = 900

CMXC = 990

MCMXCI = 1991

Some examples of invalid numbers:

IIII - you can't repeat a letter more than thrice

VL - the V, L, and D are never used to prefix a numeral

XXC - you can only prefix a single Roman numeral to a larger one

XM - X is not the next-highest numeral starting with 1; that's C

DD - you never repeat the V, L or D