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Old 09-30-2023, 02:41 AM   #20
Jellby
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Posts: 7,561
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Join Date: Jan 2008
Location: Spaniard in Sweden
Device: Cybook Orizon, Kobo Aura
Quote:
Originally Posted by Quoth View Post
The 1em = 12pt should apply on ereaders
Quote:
Originally Posted by JSWolf View Post
I thought 1em = 16pt.
What? Did I miss something?

I know the stuff with px is confusing, device-dependent and CSS-version-dependent. But I thought em and pt were well-defined and in two different worlds.

1 em is a font measure. You can think of it as "the width of the letter M" (although that's most of the time not exact). Change the font size and the size of the em changes, but will keep the relative proportions with the characters.

1 pt is a fixed absolute unit of measure, like mm and in, and it is always 1/96 in or ~0.3528 mm (https://en.wikipedia.org/wiki/Point_(typography)). Regarless of the font size.

What you can have is that by default a given reading application chooses to have fonts sized such that 1em = 12pt, but that can be changed by user and the book's formatting. If I choose my fonts to be sized at 10.5, then 1em = 10.5pt, and if there is a title sized at 200%, then inside that title 1em = 21pt, and a superscript set to 80% will be 1em = 8.4pt (or 16.8pt inside the title). And if I change the font and feel that it's too small and increase the default font to size 13, then 1em = 13pt.
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