Tuesday, August 26, 2008

Decimal time


Decimal time


In 1971, just seven weeks after I was born, Britain "went decimal". The incredibly complex and old monetary system of 12 pence to one shilling, two shillings to one florin, 30 pence to a half-crown and so on, was replaced by a very straightforward system of 100 pence to one pound. Surprisingly, there was a negative reaction among the general public, who felt that the new system was too complicated.

In the United Kingdom today, there is still some resistance to the metric system of metres, grams and litres. Since Jan 1, 2000, only metric measures can be used for trade, public health and safety, economic and administrative purposes. However, many British people still prefer to think in terms of how many stones and pounds they weigh, how many pints of beer contributed to their weight gain and how many miles they need to jog to trim their figures!

Base 10

Societies the world over are resistant to change, but the advantages of the metric system are obvious. All units are expressed in powers of 10, for example: 10 millimetres = one centimetre; 100 centimetres = one metre and 1,000 metres = one kilometre. This makes conversions of units easy because our number system uses base 10, and so multiplying and dividing by powers of 10 is simple and straightforward.

Human beings probably prefer to work with base 10 for the simple reason that we have eight fingers and two thumbs. When our ancestors counted numbers using their fingers, it was natural to stop at 10. When all the digits had been used, and to begin again, numbers were recorded as "one, ten and zero units", or 10. However, it is quite possible to work with different number bases. Computers use binary (base 2) and hexadecimal (base 16).

More than 4,000 years ago, the ancient Babylonians liked to work with base 60. They favoured factors and multiples of 60. They selected the 12 signs of the zodiac and chose to divide a full circle into 360 degrees. Because Babylonia was situated close to the equator, days and nights were of similar length and so were assigned 12 hours each, with each hour split into 60 minutes and each minute split into 60 seconds.

Metric time

In history, diverse cultures have used a variety of different units of weights and measurements. Most are now being phased out in favour of the metric system, though there seems to be little interest in introducing decimal time measures. I expect that, in my lifetime, we will convert to a system of metric time, perhaps with 10 hours in each day or night, with each hour split into 100 minutes and each minute split into 100 seconds. As a teacher of mathematics, I welcome this as it will help my pupils. Too many of them prefer to rely on a calculator rather than their brains and will unthinkingly enter "1 hour 45 minutes" as 1.45 instead of 1.75. Decimal time will also make calculations much simpler.

Of course, there are natural cycles that we cannot alter. The Earth will still revolve around the sun once every 365 days or so, and so it would be pointless to try to redefine the number of days in a year. However, mostly the daily uses of time measurement involve hours, minutes and seconds, and it is these that need to change.

Time for change?

The concept of decimal time is not new. It has been used in China, alongside more familiar units, and was also introduced during the French Revolution in 1793. Although watches and clocks were constructed showing the old system alongside the new, the idea never gained popularity and eventually died out.

I am sure that any move to introduce decimal time today would meet with the same negative reaction as the introduction of "new money" and the metric system did in England. However, we have abandoned the most arbitrary weights and measurements and now use powers of 10 in almost all of our measurement systems. For consistency, I believe we should now adopt the decimal time. The changeover might be confusing for some, but it would ultimately prove more useful.

Activity: Cartoon characters are often drawn with eight fingers and two thumbs instead of 10. It follows that they would prefer to use base 8, and would count like this: 1, 2, 3, 4, 5, 6, 7, 10, 11, 12, 13, 14, 15, 16, 17, 20, 21, ... .

They would record the number of fingers on human hands as 12 (one 8 plus 2 units). How would they record the number we write as 25? How would we write the number they record as 100?

Catherine Johnson is the head of mathematics at Shrewsbury International School. For more information or comments, you may email her at:


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