Until the 19th century recipes were very vague – ‘a goodly pinch of’ being the common type of phrase.
It seems that a US citizen named Fanny Farmer got fed up with this as it meant that cooking could be a bit hit and miss, especially cakes. So she invented a scale. She published her best-known work, The Boston Cooking-School Cook Book, in 1896. Her cookbook introduced the concept of using standardized measuring spoons and cups, as well as level measurement for all and the fact that a jug was equal to 16 cups.
Now we don’t use the cup measurement in the UK so this does tend to throw us rather when using American recipes. But as the most important things is proportion – these recipes tend to work provided you use the same cup for the whole recipe. I’ve proved this and use my ‘standard’ tea cup – I know there’s no such thing really but it’s the one I use to measure rice and so on.