How many of us have a foot a foot long?

A yard is roughly the distance between the end of your nose and the tip of your index finger, arm outstretched. But every human being’s body is not the same size. How many of us have a foot a foot long?

So King Henry I of England declared that 1 yard was the exact distance between the tip of his nose and his outstretched index finger, and wrote this definition into the statute books. At least that is the traditional story. Probably chiefs and kings had been saying for hundreds of years that 1 yard was the length between their noses and fingers. All measurements started off in a casual way such as this, and most of them were related to parts of the human body. An inch, for example, was originally a thumb’s breadth. A yard is actually twice the length of a cubit -an ancient and widely-used measurement often mentioned in the Bible. The cubit was the distance between the tip of the index finger and the point of the elbow.

A fragment of an Egyptian cubit-rod used for measurement

Measurements (and weights) needed to be standardised if they were to be of any real use. This meant making a standard unit out of something lasting, like metal or stone, and keeping it in a safe and obvious place for reference. Ancient Egyptians kept their units of measurement in the temples. In many European cities the standard unit of measurement dating back to medieval times can still be seen in a public place such as the outer wall of the cathedral in the main square. But any system of weights and measures is always being made more precise; factors such as changing temperatures, the type of materials used, and where the standard is kept, all affect its accuracy. When the British Houses of Parliament burnt down in 1834, the standard yard and the standard pound weight were destroyed, so new ones had to be made. In 1878 the British Imperial Yard was defined by law as the distance at 620 Fahrenheit between two fine lines engraved on gold studs sunk into a particular bronze bar.

During the French Revolution, at the end of the eighteenth century, Frenchmen were keen to reorganize their lives. The French system of weights and measures was most unsatisfactory, inherited, like everyone else’s, from the past. In 1790 the French government decided to bring in a new system, using logical, easy-to-handle decimals. The new unit of length was to be the meter; it would be one ten-millionth of the meridional distance from the North Pole to the Equator, measured through Paris. This gave a length fairly close to the existing French measurement, as well as to the Italian and the English.

Scientists were directed to work out the exact distance between Dunkirk, on the coast of France, and Barcelona, in Spain, from which the length of the meter could be calculated. But the calculations turned out to be much more difficult than anyone anticipated. In 1795, before the work was finished, the government decided to go ahead anyway and adopt the metric system. Four years later, the standard meter and the standard gram (the mass of a cubic centimeter of water at 40 centigrade) were officially presented by the scientists to the government. Standard meter bars were made of platinum and distributed throughout the country. However, the new system was not made compulsory, which led to a very muddled state of affairs until, in 1837, the French Parliament decided that the metric system must be the only system used in France.

Within forty years an international organization was set up to unify and improve the metric system, which had begun to be used in other parts of the world. In October 1960 the Eleventh General Conference on Weights and Measures decided that the meter should be defined as the length equal to 1,650,763.73 wavelengths in vacuum of the radiation corresponding to the transition between the levels 2p10 and 5d5 of the Krypton-86 atom. And so the business of getting more and more accurate measurement goes on.

Back in 1790 the French asked the British to join in with their new system of weights and measures. It has taken the British nearly two hundred years to agree to change. The British government has mostly adopted the international metric system. Although to this day pints, miles, inches and feet are still used everyday by the wider British public.