Metric system well worth its weight in gold

By Associate Professor Allan Blackman

This article was orignally published in the Otago Daily Times on Monday 7 October 2002.

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On August 12, lawyers for English greengrocer Steven Thoburn lodged papers with the European Court of Human Rights appealing a conviction obtained in England last year.

His crime? Selling 1.36 lb of bananas to an undercover consumer protection officer. It wasn't the bananas that were the problem, it was the fact they were weighed on scales graduated in pounds and ounces.

Britain's membership of the European Union means that, since the beginning of 2000, all traders are required to measure and report weights in metric units, and it is here that Mr Thoburn fell foul of the law — he was still using imperial measurements.

Now this might seem particularly petty. Not only that, but you're probably thinking “where's the connection to chemistry?”

It might not be immediately apparent, but chemistry is a science of measurement. We can measure the speed of chemical reactions that occur in one thousand million millionth of a second and we can measure trace amounts of chemicals to billionths of a gram.

Any measurement always consists of two parts; a number and a unit, and the former is meaningless without the latter.

One of the earliest documented units of measurement was the cubit — a unit of length used in ancient Egypt equal to the distance between the tip of the middle finger and the elbow. In fact, many units used by the ancient Egyptians appear to have been based on parts of the human body, such as the digit, the palm, the hand and the span.

Obviously, this is not ideal as people come in all different shapes and sizes. Over the ensuing millennia, a jumble of measuring systems and standards developed. For example, King Henry I defined the yard as being the distance from the end of his nose to the tip of his thumb, while Edward II decreed that three barleycorns laid end to end constituted an inch.

It wasn't until after the French revolution that a serious attempt was made to develop an international system of units. On June 22, 1799, two pieces of platinum, one weighing 1 kg and the other 1 m in length, were deposited in the Archives de la République in Paris; this was the start of what is known as the metric system, and what scientists call SI (Système International) units.

Initially, the metre was defined as being one ten-millionth of the distance between the North Pole and the Equator, but since 1983 has been defined as the distance travelled by light in a vacuum in 1/299792458 of a second.

The beauty of the metric system is its simplicity; it works in powers of 10, and uses only seven basic units, from which all others can be easily derived. So it's not necessary to remember such arcane conversion factors as 12 inches in a foot and 40 poles in a furlong.

The seven base units measure length (metre), mass (kilogram), time (second), electric current (ampere), temperature (kelvin), luminous intensity (candela) and amount of substance (mole). Knowing these, plus the various possible prefixes allows one to obtain a unit to measure any quantity.

Most of Europe and South America had adopted the metric system by 1900, and by 1960, only a few countries (mostly in the British Commonwealth) resisted the change.

New Zealand was one of the last countries to go metric, officially changing in December 1976, with the passing of the Weights and Measurements Amendment Act. The only countries apparently now not metric are Liberia, Myanmar and the United States.

But are we really a metric country? Though nobody now measures temperatures in degrees Fahrenheit, units such as feet, miles, pounds, stone, knots and acres are still commonly used. When was the last time you saw a newborn baby's weight reported in kgs? How many of you over the age of 30 know your height in metres?

The imperial system is also entrenched in common parlance — give him an inch and he'll take a mile, an ounce of luck, six feet under etc, are expressions that will probably never be replaced by their metric equivalents.

So why should we worry whether or not we use the metric system?

In 1999, a newborn baby died in England because he was given an overdose of a heart drug. The dose was measured in micrograms per kilogram of body weight, while the baby's weight was reported in pounds and ounces. In carrying out the weight conversion, a mistake was made and the baby was given 10 times the dose he should have had.

Also in 1999, the Mars Climate Orbiter spacecraft crashed into the surface of the planet due to a mix-up between metric and imperial units. While the mission specifications required metric units, engineers used imperial measurements to calculate thrust.

Or consider the 1983 case of Air Canada Boeing 767, Flight 143, which ran out of fuel at an altitude of 7925 m because the ground crew used imperial, rather than metric, conversion factor to calculate the fuel. Luckily, the pilots managed to glide the plane to safety.

These examples should hopefully convince you that we should use metric units, regardless of what misguided modern-day Luddites such as the British Weights and Measures Association (http://www.footrule.org) or the web site http://www.freedom2measure.org would have you believe.

Also, the Nobel Prize in chemistry will be announced on Wednesday — next month I'll tell you who won and why.