Quote:
Originally Posted by salamanderjuice
Pretty much every textbook should work, even at 167dpi. Most monitors and laptop screens are far below 167dpi even a 4K 27" monitor is only 163ppi. Text looks better at higher dpi/ppi but it's perfectly tolerable to read math equations on a 90ppi monitor unless they're miniscule. But you have to have the text properly rendered and not png or jpegs at whatever size the publisher decided.
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It's true about a 120 dpi screen being fine, but the size in pixels is maybe at worst 1280 x 720, typically 1920 x 1080. Or older 4:3 screens may have 1024 x768 or 1600 x 1200. The basic 6" 167 dpi ereaders are only 600 x 800. A 2K 23" screen isn't very high DPI but it's 2560 x 1440 pixels.
So an older 6" 167 dpi screen is more challenging than a cheap laptop. Even the 6" @ 300 dpi is problematic for some diagrams, equations and tables. I'd say a 7.8" or 8" at 167dpi to 300 dpi is a minimum. The DX and later screen upgrade DXG are slow and only 167 dpi, but they are 9.7"; a table or diagram on them works far better than a 6" 300 dpi screen.
Above 120 dpi the screen size is more important than dpi, though I certainly prefer 300 dpi. A fax is Letter size or A4, or even Legal size. They are 100 dpi or 200 dpi, with no shades, only black or white. The oldest eink has 4 shades and later black, white and 14 shades. If the greys are utilised in antialiasing then you've about two to three times the effective resolution compared to fax, but crippled by a 6" screen.