The problem with counting "books" is that the term is used in so many different ways, that one might end up with estimates that differ by several magnitudes depending how narrow or wide a definition or charactierization one adopts. How many books is a bible? One or around 80.[1] When there is a new minor edition, do we count no, one or 80 new books? Some of this 80 "books" are only letters and less than a page or only a few pages long. Shall we count them all as "books"? If we do so, should we than count each letter of a modern published correspondence as a single "book"? Poems were often published as very small booklets, but for prominent writers you may be able to purchase their "complete works" in a single more or less thick volumn, or the very same text in one thick volumn or a few more handy volumns. How should we count this?<p>> Physical copies. Obviously this is not very helpful, since they’re just duplicates of the same material.<p>Alas, this is quite often not the case, in particular for older books for various reasons, for example copies were bound from sheets of different print runs that used freshly assembled typesettings containing accidential or deliberate variations, sometimes sheets were missing or the order of pages is not correct, etc., etc.[2] For important "books" we should therefore digitize every available copy.<p>As great it would be to have 129,864,880 "books" scanned, this would be just an initial phase. We would need a quality control: Is the resolution of the scans really always sufficient? Are the colours correctly represented (includes every scan a standard colour chart for comparison)? What about watermarks (they are extremly important for dating old books)? ... ...<p>Besides, I personally prefer to speak of "making books digitally available" rather than of "preserving" them, because many features of a physical copy are impossible to preserve digitally: chemical coposition, (bio-)chemical traces, the DNA of parchment or animal bindings, their texture, how it feels to handle them, their visual appearance under different illuminations ... ...<p>[1] The number varies from denomination to denomination.<p>[2] And even renowned contemporary publishers sometimes silently correct errors without changing the numbering of the edition.