Simple balances have been used since 5000 BC. The equal arm balance, although updated, was the main balance used in laboratories up until the 1950s. Single pan balances were introduced in 1948. After numerous updates, these blances are still used for measuring samples of extremely small mass, according to the National Institutes of Health.
The Mettler balance is an extremely accurate piece of equipment. It can measure masses as low as 0.1 mg, according to Palomar College. Measurements using these instruments need to be fully enclosed. The sample pan needs to be brushed down before each use as these devices are so accurate that dust, air currents and even fingerprints can affect the reading, according to Dartmouth College.
Mettler balances use a balance beam with a fulcrum in the center and a pan at one end where the sample is placed. Rather than removing or adding fixed masses to the balance beam as in a normal balance, the Mettler balance exerts a force on the beam, therefore removing mass from the sample until the pan is lifted. The balance then calculates the mass of the sample and displays it as a figure.
As the apparatus uses a force to measure the mass, it is in fact a scale rather than a balance.