During this period, there was no printing press so the manuscripts were copied by the scribes by hand. The copying of the manuscripts relied upon the accuracy of the scribes. While copying the manuscripts, the scribes made unintentional errors. At times, scribes would also correct the spelling, grammar and alter what they believed to be mistakes inherent in the text. They amended apparent historical and geographical errors. These small differences grew over centuries of copying until manuscripts of the same text became substantially different from one another. As a result, historians find it difficult to use the information from the manuscript and have to read different manuscript versions of the same text to guess what the author had originally written.