From the Website by John D. Norton"Einstein's search for general relativity spanned eight years, 1907-1915. Some periods were quiet and some were more intense. The moments when the great transition occurred, came sometime between the late summer of 1912, when Einstein moved from Prague to Zurich, and early 1913. If we could choose one time at which to look over Einstein's shoulder and watch him work on general relativity, it would be this time.
And that is just what we can do. For, found among his papers when Einstein died in 1955 was a small, brown notebook containing his private calculations from just this time. This is the Zurich notebook."
"The notebook has two front covers. Einstein wrote in it in both directions. There is the front cover shown above and first here. It has Helen Dukas, Einstein's secretary's, typed description of the notebook as "Notes for Lectures on Relativity..." If we flip the notebook over, we find a second cover with the word "Relativity" in Einstein's hand." The picture shows the second cover.
Many people filled their notebooks this way, starting one set of notes from the front, and a second one from the back.