The distinction between these two terms is, for the most part, moot if you’re on the surface of the planet Earth. There is a difference of 0.5% between the gravity at either pole and the gravity at the Equator, for example, but generally speaking, gravitational differences aren’t an issue in weighing. But what if you were on the surface of the moon?

The gravity of the moon is much weaker than the Earth’s. If we consider the gravity of the Earth to be represented by the number 1, the gravity of the lunar surface is only 0.1655.
Let’s assume that we’re astronauts on the lunar surface, and we’ve just discovered a very interesting rock that we want to weigh. If we decide that we don’t want to take it into the lunar lander with us, then we need a laboratory scale that can stand alone on the lunar surface – preferably one with legs on it, to prevent contamination by the chalky moon-dust. In fact, let’s assume that we’re using an analytical scale with a chamber to prevent dust contamination. And it needs to have a reasonably large weighing capacity, because, let’s face it, rocks are heavy. (Though not as heavy as they are on Earth.)

Let’s assume that the rock would weigh exactly .375lb here on Earth. Let’s also assume that the scale was not recalibrated before the rocket took off. The astronaut would put the rock on the scale and the scale would tell him that the rock weighed 0.1655 pounds. This would not be an accurate measure of the rock’s actual weight on the Moon.

We would have to recalibrate the scale to accurately reflect the gravity of the moon. The smartest approach would be to use a calibration weight that represents the full-scale capacity of the scale on Earth. Let’s assume that the scale has a capacity of 200 grams on Earth, and we have brought a 200 gram calibration weight with us. When we recalibrate the scale, it will now read 200 grams. If we place the rock upon it, and change the factor to pounds, it would read .375lb.