How were the Original Enigma Codebooks Generated?

I have learnt a lot over the past few weeks about the Enigma Machine. One question that I can not seem to find the answer to is "How did the Germans orginally generate the the codes for the code books"? I have emailed Bletchley Park and Dirk Rijmenants nither seem to know the answer. I know that in todays world code books can be produced on a PC, but we are talking pre-computer age here. I have tried it with numbers and Letters written on bits of paper and drawn from a box. It works,but it's a bit slow, cosidering the amount of information is required to randomly draw for each day,let alone a months worth. I think that perhaps a German Military Muesum may know the answer, or is that one of lifes best kept secrets.