Many times in the past, sovereigns tried to institute the uniformity of weights and measures in the kingdom with a view to making trade easier, preventing embezzlement from unscrupulous shopkeepers and benefiting from the "national" control of weights and measures to increase their power throughout the country.

Charlemagne, in a capitular of 789, had ordered the use of identical measures in his whole empire. However, when he died in 814, the reform came to a sudden end. Then some of the kings that succeeded him attempted unification, without success. The States General held in the 16th and 17th centuries expressed this wish too, with no result.

Pile de poids de 50 marcs dite « Pile de Charlemagne », fin XVe siècle
(Paris, Conservatoire National des Arts et Métiers - cliquez sur l'image pour plus d'informations)

In 1670, Mr Mouton, an abbot, mathematician and astronomer from Lyons, suggested to adopt, as a basis of universal measures, the length of a one-minute arc of a big terrestrial circle. He called this length « milliare ». He also suggested the use of a decimal division to obtain submultiples, whose unit in use, the « virga », was equal to the thousandth of a milliare. As a control, he had calculated how many times a virga-length pendulum swang in half an hour.

Between 1670 and 1675, Picard, a Frenchman, Huygens, a Dutch and Burattini, an Italian, suggested to use, as universal length unit, the length of a pendulum with a period of one second (about 0.994 meter). However, it was found that the length of this pendulum depended on the location where it was used. Thus, in 1747, la Condamine, who had just participated in an arc of meridian measurement on the equator, suggested to specify a reference location and to choose equator for this purpose.

In 1775, Turgot, then Minister of Finance, took up again the idea of the seconds pendulum, but at the latitude 45°N. He gave Condorcet and Messier the responsibility of measuring this length, a scheme that could not be realized because of his quick resignation.

Besides, many scientists thought that the choice of the pendulum was not relevant, because it implied the obligation to specify a latitude, which might bring some countries to reject the new system.

However, the measures of Paris tended more and more to dominate the whole kingdom.

On the one hand, kings partially managed it by demanding that the same units – Paris measures – were used on the whole territory by the centralized services – such as the Forestry Commission, Mints and the service for support.

On the other hand, scientists and researchers needed a single-reference system that made comparisons easier and could be used by everyone. Therefore, they chose the measures of Paris.

Lastly, numerous merchants were using those measures, while using also the measures specific to the regions in which they traded.

That’s how the "Toise de l'Académie" and the " pile de Charlemagne" were eventually considered as France national standards.

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