No book in history has been copied as many times with as much care as has been the Word of God. The Talmud lists the following rules for copying the Old Testament.
1) The parchment had to be made from the skin of a clean animal, prepared by a Jew only, and be fastened by strings from clean animals.
2) Each column must have no less than 48 or more than 60 lines.
3) The ink must be of no other color than black, and had to be prepared according to a special recipe.
4) no word nor letter could be written from memory; the scribe must have an authentic copy before him, and he had to read and pronounce aloud each word before writing it.
5) He had to reverently wipe his pen each time before writing the Word of God, and had to wash his whole body before writing the sacred name “Jehovah!”
6) One mistake on a sheet condemned the sheet; if three mistakes were found on any page, the entire manuscript was condemned.
7) Every word and every letter was counted, and if a letter were omitted, an extra letter inserted, or if one letter touched another, the manuscript was condemned and destroyed at once.
The old Rabbi gave the solemn warning to each young scribe: “Take heed how thou dost thy work, for thy work is the work of Heaven; lest thou drop or add a letter of a manuscript and so become a destroyer of the world!”
The scribe was also told that while he was writing if even a king would enter the room and speak with him, the scribe was to ignore him until he finished the page he was working on, lest he make a mistake!
In fact, some texts were actually annotated–that is, each letter was individually counted! Thus in copying the Old Testament they would note the letter aleph (first letter in the Hebrew alphabet) occurred 42,377 times, the letter beth 38,218 times, and so on.
According to scholars Westcott and Hort, the points in which we cannot be sure of the original words are microscopic in proportion to the bulk of the whole, some 1/1000. This only one letter out of 1580 in the Old Testament is open to speculation.
*This article is from some notes I took in a “Textual Criticism” class taught by Dr. Donald Brake back in the mid 1980’s at Multnomah School of the Bible in Portland, OR.