Weights

measures used in weighing, for graduating and checking scales, and sometimes also as measures of the force of gravity (for checking dynamometers and creating loads in mechanical tests).

Scales and weights appeared several thousand years ago, with the development of trade in ancient Mesopotamia and Egypt. Ancient Babylonian, Egyptian, Greek, and Roman weights of various shapes (particularly those of sacred animals or their heads) are known. In ancient Russia, as in a number of other countries, the monetary units (coins) functioned simultaneously as measures of weight. In Russia at the end of the 18th century, spherical cast-iron weights were established in sizes of 2 and 1 pood (1 pood = 16.38 kg), 27, 9, 3, and 1 funt (1 funt ≈ 0.41 kg), and 81, 27, 9, 3, and 1 zolotnik (1 zolotnik = 4.266 g). The use of weights with these names (but in slightly different sets) continued in Russia until the introduction of the metric system.

In the USSR and other countries using the metric system, the masses of weights are expressed in kilograms, grams, and milligrams. Weights whose masses are expressed in carats (1 metric carat = 200 mg) are often used for weighing precious stones. In the USA, Britain, Canada, and a number of other countries, both metric weights and weights whose mass is expressed in pounds, as well as fractions and multiples of the pound, are used.

A distinction is made among working weights (used for weighing; there are five classes of them), standard weights, and model weights (used for checking; there are four classes). Working weights may be either separate weights or sets of weights of various masses, or built into the scales. Built-in weights are an integral part of scales; therefore, they are used and checked only in the scales in which they are installed.

Weights are characterized by a nominal mass value, a maximum deviation from the nominal value (fit accuracy), and the limit of permissible error in the determination of mass in testing. The maximum permissible deviations (Δ) for Class 2 weights are given in Table 1 as an example.

The best material for accurate weights is a platinum-iridium alloy (90 percent Pt, 10 percent Ir), from which the standard kilogram is made. Accurate weights are also made of nonmagnetic stainless steel (25 percent Cr, 20 percent Ni) and nonmagnetic chromium-nickel alloy (80 percent Ni, 20 percent Cr). Aluminum and tantalum can be used for milligram weights.

Weights and sets of weights are made with nominal mass values of 20, 10, 5, 2, and 1 kg, 500, 200, 100, 50, 20, 10, 5, 2, and 1 g, and 500, 200, 100, 50, 20, 10, 5, 2, and 1 mg. Weights of large mass (from 50 to 5,000 kg, for checking automobile and railroad car scales and for dynamometers), as well as smaller masses (to 0.1 mg, for checking and calibrating torsion microbalances), are used for special purposes.