French units of measurement

France has a unique history of units of measurement due to its radical decision to invent and adopt the metric system after the French Revolution.

Charlemagne and successive kings had tried but failed to impose a unified system of measurement in France.

[2] Although certain standards, such as the pied du roi (the king's foot) had a degree of pre-eminence and were used by savants across Europe, many traders chose to use their own measuring devices, giving scope for fraud and hindering commerce and industry.

(The Imperial pound is about 453.6 g.)[citation needed] The French Revolution and subsequent Napoleonic Wars marked the end of the Age of Enlightenment.

Talleyrand, at the prompting of the savant Condorcet, approached the British and the Americans in the early 1790s with proposals of a joint effort to define the metre.

Using Cassini's survey of 1744, a provisional value of 443.44 lignes was assigned to the metre which, in turn, defined the other units of measure.

The law 19 Frimaire An VIII (10 December 1799) defined the metre in terms of this value and the kilogram as being 18,827.15 grains.

Although thousands of pamphlets were distributed, the Agency of Weights and Measures, which oversaw the introduction, underestimated the work involved.

Moreover, the Netherlands, Belgium, Greece, Lombardy and Venice had all adopted the metric system, albeit with local names for the "metre", "kilogram" and so on.

During the early part of the twentieth century, the French introduced their own units of power – the poncelet, which was defined as being the power required to raise a mass of 100 kg against standard gravity with a velocity of 1 m/s, giving a value of 980.665 W.[16][17] However, many other European countries defined their units of power (the Pferdestärke in Germany, the paardekracht in the Netherlands and the cavallo vapore in Italy) using 75 kg rather than 100 kg, which gave a value of 735.49875 W (about 0.985 HP).

Eventually, the poncelet was replaced with the cheval vapeur, which was identical to equivalent units of measure in neighboring countries.

Woodcut dated 1800 illustrating the new decimal units which became the legal norm across all France on 4 November 1800
Table of the measuring units used in the 17th century at Pernes-les-Fontaines in the covered market at Provence-Alpes-Côte d'Azur region of southeastern France
A clock of the republican era showing both decimal and standard time .
The Paris meridian, which passes through the Observatoire de Paris . The metre was defined along this meridian using a survey that stretched from Dunkirk to Barcelona .
The Mesures usuelles were introduced by Napoleon I in 1812