In 1608 printer Hieronymus Hornschuch published in Leipzig the first editor's and printer's manual, Orthotypographia, which "while dealing mainly with the signs and symbols of correction, included short sections on schemes of imposition and type-specimens" (P.Gaskell, G.Barber and G.Warrilow, 'An Annotated List of Printers' Manuals to 1850', Journal of the Printing Historical Society, no. 4  11-31, G1).
Prior to this date no printer had published instructions any technical aspect of the printing trade—a trade which had to be learned through a presumably secretive process of apprenticeship.
Reference: Orthotypographia, by Hieronymus Hornschuch A Facsimile with a Parallel Translation of the Earliest Printers Manual, First Published at Leipzig in 1608, edited by Philip Gaskell and Patricia Bradford. Cambridge: Cambridge University Library, 1972.