What is Swatch's decimal time system called?

Swatch’s decimal time system is called Swatch Internet Time.

Introduced in 1998, the system divides a day into 1,000 equal units called “beats” instead of using hours, minutes, and seconds. One beat lasts 86.4 seconds, or 1 minute and 26.4 seconds. Times are commonly written with an at sign, such as @500 for the midpoint of the day.

Swatch designed the system to make global online communication simpler by eliminating time zones. Its reference point is “Biel Mean Time,” based on standard time at Swatch’s headquarters in Biel/Bienne, Switzerland—UTC+1. Unlike ordinary Swiss civil time, the system does not shift for daylight saving time.

Swatch Internet Time was announced on October 23, 1998, at the Junior Summit ’98. Swatch released watches displaying the format in 1999, and it briefly appeared in websites, software, and services such as ICQ. It never replaced conventional timekeeping, so “World Time,” “Metric Time,” and “Beat Time” are useful comparisons but not the system’s canonical name.