For this study, book processing was done in two steps. First, we extracted the production years and the language of digitised books from the available metadata. We disregarded books that were not tagged as German as well as those without a clear date of publication (using 15 processing rules for the dates, in addition to an extra-permissive roman numbers parser). Second, we identified the main font of the pages 10 to 19 of every book, thereby avoiding prefaces and title pages which can differ quite decisively from the rest of the book. In case the network did not detect the same font on at least 6 pages of the same book, we disregarded the entire 10 pages. This way we automatically labelled 10 pages of a total of 85’165 books as the basis for this study.