2540 dpi would equal 100 lines/mmabout the best photographic film can doand fine rotogravure printing can reproduce that exactly (they quote 2400, though). But of course, that's a small part of the publishing industry. I said 600 dpi was fine for an e-book reader. Of course, half-tone illustrations are going to be pretty badit really should be 1200 for that. There is more to books than plaintext, you know.