At first, before it was used more, the Greek alphabet, Linear A and Linear B had used a different system with symbols for 1, 10, 100, 1000 and 10000 operating with the following formula: | = 1, – = 10, ◦ = 100, ¤ = 1000, ☼ = 10000.[1]
The earliest alphabet-related system of numerals used with the Greek letters was a set of the acrophonicAttic numerals, operating much like Roman numerals (which derived from this scheme), with the following formula: Ι = 1, Γ = 5, Δ = 10, ΓΔ = 50, Η = 100, ΓΗ = 500, Χ = 1000, ΓΧ = 5000, Μ = 10000 and ΓΜ = 50000.
The acrophonic system was replaced by a new alphabetic system, sometimes called the Ionic numeral system, from the 4th century BC. Each unit (1, 2, …, 9) was assigned a separate letter, each tens (10, 20, …, 90) a separate letter, and each hundreds (100, 200, …, 900) a separate letter. This requires 27 letters, so the 24-letter Greek alphabet was extended by using three obsolete letters: fau ϝ, (also used are stigmaϛ or, in modern Greek, ΣΤ) for 6, koppa ϟ for 90, and sampi ϡ for 900.[2] To distinguish numerals from letters they are followed by the "keraia" (Greek κεραία—insect antenna), a symbol similar to an acute sign (Unicode U+0374).
Fau (also spelled vau, pronounced wow) may also be called digamma. The two are the same in meaning, and either symbol may be used to represent the number 6.
This alphabetic system operates on the additive principle in which the numeric values of the letters are added together to form the total. For example, 241 is represented as ΣΜΑʹ (200 + 40 + 1).
To represent numbers from 1,000 to 999,999 the same letters are reused to serve as thousands, tens of thousands, and hundreds of thousands. A "left keraia" (Unicode U+0375, ‘Greek Lower Numeral Sign’) is put in front of thousands to distinguish.