Today the European Union announced that it gave Britons permission to keep their imperial units in parallel to the metric system forever. This reminded me of a statement in my lecture 21: "Since 1975, when Britain, Canada and Australia finally converted to SI units, the USA remain the only scientifically and economically important country that does not use SI units." I noticed that I was giving the British government more credit than it deserves.
Britain changed from the Pound/Shilling/Pence currency system to the decimal Pound/Pence system in 1971, but that was about it. Distances are still in miles, volumes in pints and gallons (though different from US pints and gallons), weights are in ounces and pounds, and the list goes on ...
I changed the text in lecture 21 to: "Since 1975, when Canada and Australia converted to SI units, Britain and the USA remain the only scientifically and economically important countries that do not use SI units."
In Britain, labelling and measuring in metric has been compulsory since 2000, but not in the USA. The reason for this difference is very simple: 88% of Britain's trade is with metric countries, and Britain's industry would experience a great disadvantage if it continued to offer goods based on imperial measurements. In contrast, the economy of the USA is based on a very large domestic market, while the export of goods made in the USA represents only a minor component. The US-American manufacturing industry considers the continued use of imperial measures a shield against imports from metric countries.
While I was going through the lecture I noticed the sentence: " There had to be an end to inches, Zoll, furlongs, yards and whatever other units of length were in use across Europe." Inches, furlongs and yards are British measures, Zoll is German. The German measures disappeared from use when Napoleon occupied the country and reorganized its administration, but inches, furlongs and yards are still alive. To move my sentence closer to reality I replaced the British measures by the French length measurements league and pouce and threw in the German Elle for good measure: " There had to be an end to league, Zoll, pouce, Elle and whatever other units of length were in use across Europe."