Slant: how far the letters lean

How font.io measures slant — the lean of the lowercase l in degrees, fitted through the middle of its stem.

Inter Italic: 9.4° — italic. Inter Regular: 0° — upright. Slant is the lean of the letters, in degrees from vertical. Near zero is upright; a rightward lean is italic; a leftward lean (rare) is a backslant.

Slant: fitting the stem

Inter Italic ‘l’ — five stem centers across the interior rows (25–75% of the ink height), a least-squares line through them, and the angle from vertical

Interior rows only, so terminals and serifs can’t pull the fit. Degrees from vertical, + = leans right. This outline-based fit agrees with measure.py to a tenth of a degree.

How we get the number: take the lowercase l and find the horizontal center of its stem at five heights. Fit a straight line through those five centers and measure the line’s angle from vertical. Sampling the middle of the letter — not the top and bottom — keeps swashy terminals and chunky serifs from pulling the estimate.

A real example: Inter Italic’s l leans 9.4° — italic. Inter Regular’s sits at 0.0° — upright.

One caveat: if the five stem centers don’t sit on a straight line — a swashy decorative l, say — we flag the number. The reported lean is still the best single summary of the overall slant; the flag just notes the stem curves.