Table numbers need tabular figures or the column will not line up

What it is

In most body faces, digits are proportional: 1 is narrow, 0 is wide. Drop them into a table column and place values no longer stack; a units-place 1 slides in under the tens. Tabular figures give 0–9 a shared advance width, so the column becomes a scannable place-value grid. That is not the same as right-aligning the column. Alignment chooses which edge the run sits on. Tabular figures decide whether each place still shares a vertical.

Why it happens

Reading a table is a vertical comparison: which row is larger, do the points line up. Comparison needs place value — units, tens, hundreds at fixed x positions. Proportional digits knead that grid away, and columns full of ones (indices, percents, years) look as if they were falling diagonally. Tabular figures are a second set of glyphs, usually shipped with lining figures (cap-height). Oldstyle figures bounce on the baseline even when tabular, so a scan is still interrupted by extenders; tables default to tabular lining. In OpenType this is a feature such as tnum, not “switch to a monospaced English face,” which would also freeze the letters and make surrounding copy ugly. Only the digits need to go tabular; Latin words can stay proportional.

Where it stops holding

Years, house numbers, and quantities passing through a sentence belong in proportional figures; forcing tabular there leaves odd holes between words. Tabular ones carry extra sidebearings, so a large run of them can look sparse. Equal width is not equal colour: 1 is still lighter than 8, a weight issue, not a width issue. A display face with no tabular set should not be asked to set a column that has to align.

Applying it

• Turn on tabular figures (or pick a face with tnum) for price columns, indices, and stats. Do not use the body’s proportional digits there.
• Set a column that mixes 111 and 800 and look at the units place. If it jumps, proportional figures are still on.
• Leave proportional figures in running prose. Do not lock font-variant-numeric globally for the sake of one table.

Related

• Same group: F4.18.2 Money and serials should sit on the trailing edge so places can be compared · F4.18.3 Uneven fractional digits break the point of a vertical comparison · F4.18.4 Space and wrapping between a number and its unit need their own rules
• Nearby: F4.05 Alignment · E4.03 Tables
• Search terms: tabular figures · lining figures · tnum