Church Slavonic has no separate digits. Numbers are written with the letters of the alphabet, using the Greek system, and the arrangement repays a moment of attention because a reader who does not know it will misread dates and chapter numbers without any sign that anything has gone wrong.
Nine letters carry the units, nine the tens and nine the hundreds. A letter doing duty as a number takes a titlo, a stroke drawn above it, which is the only mark distinguishing the numeral from the sound. Thousands are marked by a small slanting sign written below and to the left of the letter, so the same nine unit letters serve again at a scale a thousand times larger. There is no zero and no place value: the system is additive, and a number is simply the letters for its parts written together.
Two features regularly catch a modern reader out. The teens are written with the unit before the ten, matching the way they are said aloud in Slavonic, so the letters for four and ten in that order mean fourteen rather than forty one. And years in the church books are counted from the creation of the world on the Byzantine reckoning, not from the Incarnation, which puts them some five and a half thousand years ahead of a modern date.
The letters that carry no number are as informative as those that do. They are the signs supplied for Slavonic sounds after the Greek series had been allotted, and they mark, silently, where the borrowed alphabet stopped and the new work began.