Decimal time

1000 metres in a kilometre, 1000 grams in a kilogram, and 1000 minutes in a day?

You all know that I’m a fan of the metric system (see metric martians and the metric highway). We have metric measurements for mass, length, temperature… it makes conversion and calculation so easy. Measurements go up by increments of a thousand, and they go down by increments of a thousand.

Except for time. There are 60 seconds in a minute, 60 minutes in an hour, and 24 hours in a day, and the metric system has not changed that. (Funny story, while this division of time dates back to the ancient Sumerians, the second was of no use historically and only began to be measured with the arrival of mechanical clocks in the 15th century CE.) In revolutionary France, the new authorities did in fact experiment with a new set of measurements for time: decimal time.

This is the system: 10 decimal hours in a day, each hour 144 of our minutes long. The decimal hours were divided up into 100 decimal minutes, each 86.4 of our seconds long. The decimal minutes were 100 decimal seconds long, which meant the seconds were actually shorter than ours.

This system has many advantages: you can add and subtract time given in hours, minutes, and seconds easily and quickly. This post – like all posts on this site – is published at 7am Auckland time. In decimal time, that would be 2.91.66 (the 66th second of the 91st minute of the 2nd hour of the day).

Beginning in 1792, the French gave it a good shot – decimal clocks like the one pictured above were even made – but it never caught on and was abandoned in 1795… just as the metric system itself was being born.

• Decimal time
• History of timekeeping devices