In the cooking class I went to, we were told that a plastic measuring 1 cup held less then the metal 1 cup . We tested a lot of 1 cup measuring cups. The metal one always held more. It was only the one cup measure. Odd. I always use the metal ones for measuring since then. If you have both check that out. Also it is surprising how many do not know liquid measures need liquid measuring cup not dry measuring cups. For the most part the foods baked/cooked are fine with not precise measures. To give the food the best chance to be excellent then it's best to be precise.