Tischendorf believed that four separate scribes (whom he named A, B, C and D) copied the work and that five correctors (whom he designated a, b, c, d and e) amended portions. He posited that one of the correctors was contemporaneous with the original scribes, and that the others worked in the 6th and 7th centuries. It is now agreed, after Milne and Skeat's reinvestigation, that Tischendorf was wrong, in that scribe C never existed. According to Tischendorf, scribe C wrote the poetic books of the Old Testament. These are written in a different format from the rest of the manuscript – they appear in two columns (the rest of books is in four columns), written stichometrically. Tischendorf probably interpreted the different formatting as indicating the existence of another scribe. The three remaining scribes are still identified by the letters that Tischendorf gave them: A, B, and D. Correctors were more, at least seven (a, b, c, ca, cb, cc, e).