My friend, who has been researching basic physics, is saying the following, which I frankly had never heard of: We use metric and imperial measurements interchangably (I weigh 82kg or 180 lbs, same diff) but they are not at their essense the same thing. Pounds measure weight - our weight here on Earth (an effect of the gravitational pull of the Earth), whereas kilograms are intended to measure mass (a property of the number of atoms in the sample, independent of gravity). The distinction is largely academic, but it is real. I do not doubt her knowledge, I have just never heard of this distinction. Is there truth to this? Please don't misunderstand my question: I have no doubt whatever about the difference between weight and mass, my doubt is about the unit of measurement being pounds vs. kg.