Quote:
Originally Posted by DNSB
The fixation that if it looks good as a pBook, it's going to look good as an eBook. The people reading ebooks on different devices will not change fonts, font size, line spacing, margins, etc.
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For people with vision difficulties, the fact that most eBooks use "em" as the unit for spacing just makes their lives even more difficult.
With an "average-sized" font, an 8em left margin for something like a poem isn't a problem. Crank the base font size up by just 2x and that left margin is now at the center of the screen on a 6" device, assuming minimal device margins. So, now that line will hold just a handful of characters before it hits the right margin, especially if that margin is set to make the text indented on both sides.
The same goes true for vertical margins, especially for chapter numbers. Those usually start bigger anyway, so now a 6em margin-top plus a 3em margin-bottom turns into (6 + 3) x 1.5 (chapter font size) x 2 (scaling chosen by the user) == 27 "average-height" lines, when a 6" reader can display about 25 "average-height" lines on a single screen.
Using "%" for spacing generally works out better for accessibility, since it's always based on the parent element size. So, a 15% margin-top will always be 15% of the screen height (ignoring device margins), even if the base font size gets increased.
Some publishers use "%" for vertical spacing (and even those don't use it in every instance), but almost none use it for horizontal spacing.