-- Mass can be measured using a balance.
(It's not the only way.)
-- The mass of an object remains constant,
no matter where it is or what it weighs.
-- The "kilogram" is the international standard unit of mass.
A kilogram of mass weighs about 5.8 ounces on the moon,
about 13.3 ounces on Mars, about 2.2 pounds on Earth . . . . .