I've been playing with the PDF approach plates. Well rendered they are
easily readable at 600x800 (they're taller than they are wide, but
narrower than the 4:3 aspect ratio of most display) with 16 levels of
grayscale. 480x640 is pretty good with 16 levels of gray, down to right
on the ragged edge of usable with only 4 levels.

The device doesn't need that much storage. A largish compact flash card
should hold all of the pages on the entire DVD if they're pre-rendered
(a GIF of the plate is much smaller and displays much faster).

What it does need is a reasonably large screen, probably at least 6"
diagonal. There are some 480x640 PDAs, but they have very small screens.
There are tons of 240x320 PDAs but I don't think they'd ever be suitable
for viewing plates.

I'd rather avoid a laptop or even a full tablet PC (stuff with 10"+ screens)
in favor of an ebook/pda sort of form factor.

--
Ben Jackson

http://www.ben.com/