Recipe Scaler

In short Scaling a recipe means multiplying every quantity by the ratio of new servings to old, and the reason to use a tool rather than mental arithmetic is that the result should stay READABLE. Two-thirds of a cup is a measurement you can execute; 0.667 cups is not, and this returns ½, ⅔ and ¾ because that is what measuring spoons and jugs are marked in. Three things do not scale linearly and the tool deliberately leaves them alone. Cooking time barely changes with quantity — a double batch of biscuits takes the same time, because the thickness has not changed, while a double-depth cake takes considerably longer at a lower temperature. Salt and strong spices scale less than proportionally; doubling a curry rarely wants double the chilli. And leavening in baking is closer to a proportion of the flour than a free variable, so doubling it is usually a mistake. If a line was left untouched, it is because no quantity was recognised in it — quantities written in words, ranges like "2 to 3 cloves", or amounts embedded mid-sentence are the usual cases, and they are worth checking by eye before you start cooking.