An object placed on an equal-arm balance requires 12 kg to balance it. when placed on a spring scale, the scale reads 12 kg. everything (balance, spring scale, set of masses and object) is now transported to the moon, where the force of gravity is one-sixth that on earth. the new readings of the balance and spring scale (respectively) are:

equal-arm balance = 12 kg spring scale = 2 kg The equal arm balance measures the mass of an object by using a counter mass on the opposite plate of the balance. The force of gravity affects both the mass being tested and the mass standards being compared against equally. So if the local gravitational field changes, those changes affect both the tested mass and the standard masses equally. Contrast that to the spring scale. In that scale, the spring provides a calibrated level of force irrespective of the local gravitational field. So if the local gravity is higher, the force indicated also is higher. And if the gravitational field is lower, the indicated force is also lower. The strength of the spring DOES NOT CHANGE with changes in the local gravitational field.