That's great and all. But by measuring everything in millimetres and grams you miss out on the very thing that makes the metric system great; the easy conversions. You can measure things in millimetres and easily switch to centimeters, just by moving the decimal sign, when the measurement gets large enough. That way you can almost always keep the numbers manageable. No need to say 1500 millimetres. Just say 1,5 m.