A few days ago, it was published on BLOC@CACM that a lost user manual
for the Z4 and notes on flutter calculations was found in the ETH Zürich
archives. See:
https://cacm.acm.org/blogs/blog-cacm/247521-discovery-user-manual-of-the-oldest-surviving-computer-in-the-world/fulltext
Zuse Z4, a relay computer of 1945, however, due to lack of
documentation, its functionality was largely unknown. Now a manual for
the machine has appeared at ETH Zurich, that was buried in the archives.
And this in the digital age ...
Thomas