I think the most convenient way is the metric system. You had 1.5 desiliters of milk and 4 desiliters of sugar, but want to a half batch instead? Must be 0.75dl and 2 dl then
Metric or imperial doesn't really make a difference here.
Say the recipe is for five things and you want to make twelve.
You've got the same scaling problem no matter how you measure. You don't get "metric eggs", so solving "it needs two eggs for five so how many eggs for twelve" is the same.
