Platform 05
Optical centring
Each number is measured in the page: the baseline comes from a zero-size marker on the text, the cap height is 1490/2048 of the font size, and the number is how far the middle of the capitals sits from the middle of the box, positive when they sit low.
From the Engineering page on ramtt.com
- Inter's ascender minus its descender equals its cap height (1984 − 494 = 1490 units), so an untrimmed line would centre capitals exactly, but Chrome rounds ascent, descent and leading to whole pixels, which moves them 0.27 to 0.37 px here.
- Trimming with text-box: trim-both cap alphabetic cuts the box to the capitals and the baseline, 13.5 px off the heading's 28 px line, so the box is the ink and the offset is zero to Chrome's 1/64 px layout unit.
- Without text-box a script makes the same cut with negative margins taken from the cap height and the measured baseline.