While Americans still cling doggedly to non-decimal measurements like gallons, pounds and miles, in Europe the era of decimalisation has become firmly established. The litre, the gram and the the metre have become the main units of measurement across most of the continent; only the UK seems to retain a sentimental attachment to the old imperial measurements - ask most British people to tell you their height or weight and the answer will almost always come in feet and inches or stones rather than metres and centimetres or kilograms.

However, one thing that has not been standardised to a decimal unit of measurement is time. Clocks still use 12 or 24 hours, 60 minutes and 60 seconds. This means that calculating the length of time between two given points can involve quite complicated calculations. So why has the practice of using these odd measurements of time persisted throughout history?

It is not at all clear why human beings started to measure days in units of twelve, 24 and 60. One plausible theory, though, is that the ancient Babylonians - from whom much of our system of time and date recording seems to derive - counted the hours using their fingers. They counted them, however, rather differently to the way we count on our fingers today. The Babylonians, it is thought, used each individual segment of their index, middle, ring and little fingers to represent a unit. Since each finger has three segments, this makes two sets of twelve units.

If you use just one hand to count up to twelve, and use the five fingers of the other hand to keep track of each set of twelve units, you can easily count up to 60. This is a simple method of using the fingers to count in the duodecimal system used by the Babylonians. To them it probably seemed as easy and intuitive as the ten unit decimal system we are familiar with today.

Over the centuries there have been various attempts to standardise time on a decimal basis. One of the earliest took place during and after the French Revolution, between 1793 and 1806. During this time the day was divided into ten hours, each lasting for 100 minutes. Each minute was in turn divided into 100 seconds, making the total length of the day 100,000 seconds.

In addition to reforming the clock, the French Republicans also instituted a new calendar. The year consisted of 365 or 366 days, which were split up into 12 equal months lasting 30 days each. To make up a full year it was necessary to add either five or six additional days after the end of the twelfth month. The year began on the anniversary of the establishment of the Republic on September 22, 1792.

The Republic's new official time keeping procedure kept going for more than ten years, but eventually - as the rest of the world showed no interest in switching to decimal time - France reverted to the old 24-hour day.

Other attempts have been made over the years to introduce a decimal system, most recently by Swiss watch maker Swatch, which invented a new unit of time measurement called the beat, with each day consisting of 1,000 beats. So far, however, this system would appear to be going the same way as the French Republican calendar.