For other meanings of the word balance, see:
A balance (also beam balance or laboratory balance) is used to accurately measure the mass of an object. This class of measuring instrument uses a comparison technique in its conventional form of a beam from which a weighing pan and scale pan are suspended. To weigh an object, it is placed on the measuring pan, and standard weights are added to the scale pan until the beam is in equilibrium.
Very precise measurements are achieved by ensuring that the fulcrum of the beam is friction-free (a knife edge is the traditional solution), by attaching a pointer to the beam which amplifies any deviation from a balance position; and finally by using the lever principle, which allows fractional weights to be applied by movement of a small weight along the measuring arm of the beam.
While the word "weigh" or "weight" is often used, any balance scale actually measures mass, which is not dependent upon the force of gravity, as opposed to a scale with a spring, which measures weight. Mass is properly measured in gramss, kilograms, pounds, ounces, or slugs; while weight is in newtonss or pound force.