Iota and the Coptic Numeral Decades

The Coptic numeral system, inherited entire from Greek, works in three ranks of nine. The first nine letters of the alphabet count the units from one to nine; the next nine count the tens from ten to ninety; the last nine count the hundreds from a hundred to nine hundred. Iota stands at the head of the second rank, so it is the point where the counting changes gear. This arrangement requires twenty seven signs, and since the Greek alphabet in ordinary use has only twenty four, three extra signs were needed. Coptic took all three: sou for six, and the archaic Greek numeral signs for ninety and nine hundred, none of which writes a sound in any Coptic word.

The seven letters Coptic added from Demotic sit outside the numeral system altogether and carry no value, because they were never part of the Greek series from which the values come. That is a distinction worth stating plainly, because it is easy to assume that every letter of an alphabet with numeral values must have one. Coptic numerals appear constantly in manuscripts, marking quires, folios, chapters and psalms, and in dates reckoned by the Coptic calendar, whose era of the martyrs counts from the accession of Diocletian and is still in liturgical use in the Coptic Orthodox Church. A stroke drawn above a letter tells the reader to take it as a figure.