The official introduction of the metric system in September 1799 was unpopular in large sections of French society. Napoleon's rule greatly aided adoption of the new standard not only across France but also across the French sphere of influence. Napoleon ultimately took a retrograde step in 1812 when he passed legislation to introduce the mesures usuelles (traditional units of measurement) for retail trade—a system of measure that resembled the pre-revolutionary units but were based on the kilogram and the metre; for example the livre metrique (metric pound) was 500 g instead of 489.5 g—the value of the livre du roi (the king's pound). Other units of measure were rounded in a similar manner. This however laid the foundations for the definitive introduction of the metric system across Europe in the middle of the 19th century.

When was the metric system officially introduced?