Unusual UPM value

Definition

Units-per-em (UPM) sits outside the typical 1000–2048 range. Most foundries pick 1000 (PostScript convention) or 2048 (TrueType convention). Unusual values still work but may cause off-by-one rounding when other tools assume a standard UPM.

How Patens surfaces this

The Patens audit module checks for upm-unusual across five teaching surfaces: the edit-panel inline issue list, the project-wide audit page, the release pre-flight check, the family hub, and the home-page project tile. Every surface shows the same plain-English explanation and links back to this page. This rule is detection-only — there's no automatic fix because the correction is design-dependent (it requires a judgment call about the glyph's intended shape or the font's intended behaviour). The audit message links to the specific glyph or field that needs attention.

Run this check yourself

Patens runs every audit rule live as you draw — including this one. The editor (in private alpha) shows upm-unusual firing on real glyphs, or check your own work from the CLI:

npx patens audit your-project.font.json