A very informative book published by German Intelligence in 1916 on the Russian Order of Battle. The book is a treasure trove of unit information down to regimental level. Information inlcudes the regiments higher HQ and their regimental cyphers. Found at the TMCA show in Franklin, TN.
I managed to pick up a copy of the self same edition some years ago. I was fortunate to also receive with it a supplement of about 40 pages dated July 1917.
The Austro-Hungarian intelligence department also produced a similar tome. This from 1917: