The stories behind the marks.

Both marks are centuries old. Early modern mathematicians — Napier's works among them — used the point and the comma alike, and Europe simply standardised in different directions: the English-speaking world settled on the point, most of continental Europe on the comma. Neither is more correct; ISO accepts both.

So roughly half the world reads 1,5 as one-and-a-half, and the other half reads the very same characters as fifteen. It is the single most dangerous ambiguity in written arithmetic, and it lives in one keystroke.

The United States says July 6 and so evolved 7/6; most of the world says 6 July and writes 6/7. For two-digit days and months the two orders are indistinguishable — and silently wrong.

ISO 8601, first published in 1988, is the peace treaty: 2026-07-06, biggest unit first. It sorts correctly as plain text, and it is ambiguous never.

ISO 8601 says Monday. Calendars in the US, Canada and Japan traditionally show Sunday first — an inheritance from religious week-reckoning. Every calendar app you've ever used quietly consults your locale to decide which column comes first.

The same number wears local dress: 1,234,567 in New York; 1.234.567 in Berlin; 1 234 567 under SI's recommendation of a thin space; and 12,34,567 in the Indian numbering system — groups of two after the first three, because the system counts in lakhs (100,000) and crores (10,000,000).

All four are the same value. Only the grouping tells you where it was written.

All of the above lives in the Unicode Common Locale Data Repository — the open database that phones, browsers and operating systems consult so that Iceland's dates, India's digit groups and Austria's decimal commas all come out right. It's why your phone already knows conventions you've never heard of.

This site reads from the same book: every example is derived from CLDR 48.0 at build time, never transcribed.