The Scribes are called Sopherim in Hebrew. Sopherim derives from the Hebrew verb saphar “to count”. The scribes used a number of methods to ensure that the text did not change but stayed the same.
They counted each and every letter in every book of the Old Testament. They counted every word and every letter in every book to ensure none were lost. When they had finished they looked for the middle word in each book and they marked it accordingly. They also determined the middle letter of every book and marked that too. In addition to that the frequency of all letters was recorded.
The text of the book of Genesis consists 76.064 letters and 1,534 verses
The middle clause of Genesis is found in Gen 27:40
“You shall live by your sword”
The middle word is your sword (חרבך)
The middle letter is ב
So the middle letter was marked accordingly with a marginal note showing the middle letter. The middle word was also recorded but of course the middle letter was not necessarily found in the middle word. The middle letter could be found in a different word from the middle word.
The count of each Hebrew letter was recorded across each book to indicate this book has been checked and all words and letters are present and accounted for. If the count was not substantiated then the scroll was abandoned and a new scroll started. There are 815.140 in the complete Old Testament text.
After the total of all letters was determined the scribes then counted the total of each letter individually. Every B, C, D etc. Only the consonants were counted, not the vowels. Hebrew vowels are written by a dots and dashes under the letters. After this was done for each and every book, the frequency of letters were recorded and kept with the scroll to record the accuracy of that particular scroll
Ketiv / Qere
The scribes derived a system called Ketiv Qere to handle what they considered to be discrepancies in the text.
Ketiv (K) from the verb to write meaning “that which is written”.
Qere (Q) from the verb to read meaning “what ought to be read”.
Under the system of Ketiv Qere, marginal symbols were used to mark textual discrepancies. Ketiv (K) dan Qere (Q) are marks made on suspect letters or words which were then connected to marginal notes. See the example below, contrived from Number 6:24-26.
May the LORD bless you and protect you.
MyK1 the LORD smile on you and be gracious to you. Q1 - may
May the LORD show you his favour and liveK2 you his peace.’ Q2 - give
Imagine for a moment a scribe coming across a mistake in the text where ”my” should read ”may” and again where ”live” should read ”give”. If a scribe came across such a reading as that, he would mark the suspected mistake with a Ketiv and then in the margin make a correction marked with Qere. No scribe would dare to change the word in the text of Scripture himself. So in the text the ketiv would signify ”what is written” is this but I think ”what ought to be read” is that. Each scribe had a high view of the text of YHWH he was copying and he was not willing to make a change to the text himself even though it might seem obvious. The scribes remembered Uzzah who reached out to touch the Ark of the Covenant when it was forbidden to do and was killed by God. No scribe would dare alter the text without a Ketiv – Qere for fear of being struck down.