Balance

A balance or 'laboratory balance' is used to accurately measure the weight
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.