Wow!! All this because way, way , way back in the day, America decided that it didn't want to go metric.
America didn't see the benefit in World wide trade opportunities, that would have resulted in a standardization of packaging for export. A lot of products could have been sold in the same packaging, if properly labeled for the jurisdiction of sale.
America only saw the expense of re-tooling packaging and production.
Americans never saw the difference in the size of a shot of liquor between U.S. Ounces and Imperial ounces. ( that's too bad!
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Americans didn't much see the benefits of a standardized measuring system. Even something as simple as a recipe.. SO much easier not to wonder what format is being used ( U.S. , Imperial, or Metric).
1 U.S. Gallon. = 3.78541 Liter
1 U.S. ounce. = .02957 Liter
1 Imperial Gallon. =4.546 Liter. ( That's why my car gets better mileage in Canada, than in the U.S.)
1 Imperial fluid ounce to Liter. .02841
1 imperial fluid ounce to Imperial quart. .0300 ml.
Etc., etc., etc.,
No matter what, I respect my American neighbour's choice to not participate in Metric standardization. And, I was born ata time that I learned all three systems. So, for me, it's not an issue.... But I could see, that for some,, it's a big pain. Especially when you can't be sure of the original measuring system.