You used to be able to stick a lot of text on a 320x200 display when I first got into software development. :)
Jokes aside, you'd probably want that 480x800 (portrait rather than landscape). Which would be 80 columns and 100 rows in old 8-bit microcomputer terms. So it wouldn't be the more detailed of a document but it should be detailed enough for a cheat sheet or narrowly focused reference page. You probably wouldn't want much more than that anyway otherwise you risk your reference material to be too verbose for quick sanity checks.
I'm always surprised that e-ink readers have such good readability at low resolutions. I think an accidental by-product of how they work is a little "fuzziness" when translating from digital data to analog atoms, so the text looks more like organic newspaper ink than a pixellated screen.
Anyway, most e-readers are in the ballpark of 800x600; and I expect if the concept got traction, there's no reason it couldn't be scaled up to 8.5" x 11" at equivalent pixel densities (at the cost of hovering your phone for a few seconds longer or whatever).
> Anyway, most e-readers are in the ballpark of 800x600
A Kindle Paperwhite is 1072x1448, 300 PPI, 16 levels of grayscale.
I personally couldn't tolerate reading on a kindle until they reached 212 PPI. 800x600 may be acceptable for a simple sign, but it's not gonna wow anyone.
I think you must be spoiled by modern high-dpi displays if you can't see any use for 800x480 displays. When I was in school I used to put cheatsheets on my TI-83+ which had a 96×64 monochrome display!
