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Codes & LettersCiphers, scripts, symbols — every code humans write, taken apart.

Definition

The Eye's Thumb on the Scale

Updated

The eye's thumb on the scale is the name Codes & Letters gives to optical correction in letterforms. Shapes that are equal by measurement can look unequal to the eye, so type designers adjust them until they look equal. Think of it as a designer pressing a thumb on the scale on the eye's behalf. The phrase is this site's own label for the group as a whole, not a replacement for established names such as overshoot.

What the term covers

Codes & Letters groups three corrections under the term: overshoot, visual centering and counter compensation. Each is a case of shapes that are equal by measurement looking unequal to the eye.

Overshoot works on height. A curved letter drawn exactly as tall as a flat-topped one tends to look smaller, so its curves run slightly past the guidelines, above the capital height and below the baseline. Counter compensation works on counters, the areas of a letter that its strokes fully or partly enclose.

Overshoot in Noto Sans

Compare a capital O with a capital H in Noto Sans Regular, on the font's grid of 1,000 units per em:

LetterBottom of outlineTop of outlineTotal height
H0714714 units
O−10725735 units

The H sits on the baseline and stops at 714, which is also the capital height recorded in the font's OS/2 table. The O overshoots by 11 units at the top and 10 units at the bottom, about 1.5% and 1.4% of that 714-unit capital height.

The figures come from the Noto Sans variable font, Version 2.015 (NotoSans[wdth,wght].ttf from the google/fonts repository, downloaded 2026-10-04), at weight 400 and width 100, with the outline bounds read from the font file by a program. Noto Sans is released under the SIL Open Font License, Version 1.1.

These numbers hold for one font, one weight and one version. The FontForge glossary notes that the amount of overshoot changes with type size, so the figures are not a rule for all type, and another font or weight needs its own measurement.

Limits of the term

The eye's thumb on the scale names a group of design corrections. It is not a law of perception and not a measurement in itself: any figure given for it belongs to the font, weight and version it was measured in.

How measurements on the site are made: About Codes & Letters. Other terms used on the site: letter debt and frequency fingerprint.

Sources