Strolling through the exhibition on Bad Mergentheim's history I suddenly was thunderstruck. Behind an old cupboard only half visible I read the word "Maaß" on a poster and rapidly figured out that it didn't mean a Maß of beer but an information panel introducing metric measures and weights as recommended by the authorities on 29 March 1870 for use in Baden's primary schools. Up to now I always had assumed that the metric system had been introduced in Germany with its unification in 1871. Looking up Wikipedia I read that the 2nd Reich had adopted the metric system indeed on 1 January 1872 but how to explain its earlier introduction in Baden at the eve of the start of the French-Prussian war in 1870?
The poster illustrates how up to 1870 technical exchange and trade between German territories were hampered by the use of feet having various lengths. In fact, the foot varied from a meager 0.25 m in the Duchy of Hesse-Darmstadt to an enormous 0.3161 m in the Austrian Empire with the English foot of 0.3048 m in between. The foot in the Great Duchy of Baden measured exactly 0.3 m. Both Hesse's and Baden's feet are a clear deference to Napoleon's Rheinbund making the lengths easily convertible into the meter that France had introduced as early as 1799.
Other European countries have adopted the metric system well before Germany like the Benelux (Belgium, Luxemburg) in 1820, Switzerland 1835, and Italy 1861 following its unification. The UK is still in changeover to the metric system and the US Congress passed a Metric Conversion Act as late as 1975 with apparently no changes so far as the daily life of the US citizen is concerned. The Wikipedia page gives a lot of anecdotal information about the history of the metric system.
The metric system is not without flaws. I do not mean that the statement found on the poster one meter being the 1/40 000 000 part of the earth's circumference was wrong from the start* but that the basic unit of weight is the kilogram i.e. a metric quantity with a prefix. This is due to the fact that the initial French system had retained specific and sometimes traditional names for the new metric quantities. The basic unit for the weight (today it is rather defined as mass) was called the grave and one thousandth of it was the gram. Since grave sounded too aristocratic the name was abandoned in the course of the French Revolution.
*since 1983 one meter is defined as the distance light will travel in vacuum during 1/299 792 458 seconds
A simelar use of traditional names for the new lengths in German is found on the poster. One centimeter is called Neuzoll (new inch), ten meters are a decameter or a Kette (chain) and one kilometer is named Wegstrecke (length of way or path). These names never made it into common use.