French Decimal Time Converter

Along with the metre and the kilogram, revolutionary France decimalised time: a decree of October 1793 divided the day into ten hours, each of a hundred minutes of a hundred seconds. That gives a hundred thousand decimal seconds a day, against 86400 in the sexagesimal system. The decimal hour runs 2 hours 24 ordinary minutes, the decimal minute 86.4 seconds and the decimal second 0.864 of a second.

It did not last. It became optional in April 1795, under two years later, and fell out of use — the only piece of the metric system to fail outright. The reason is mundane and instructive: replacing rulers and scales is cheap, replacing every clock in a nation is not. The few surviving dual dials, ten hours on the outside and twelve within, now fetch a fortune at auction.

What remains is a lesson in why some units resist decimalisation. Length and mass are private quantities: you measure alone and the result depends on nobody. Time is coordination — it only works if everyone agrees, and the cost of switching grows with the number of people involved. It is the same reason the Swatch beat, which in 1998 tried the same thing with a unit of exactly 86.4 seconds, also failed.