Metric system
There are 16 US fluid ounces in a US pint but there are 20 imperial [UK] fluid ounces in an imperial pint. The US fluid ounce is larger than the imperial fluid ounce, but the imperial pint is larger than the US pint.  In the 1700's this type situation was common across Europe. Each country  measured length, weight/mass and volume in its own way. Sometimes different countries or cities used the same name for different measurements.   Sometimes different cities in the same country had different ways of measuring things. In 1789 there were a quarter of a million different units of weight and measure in France.