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This heading covers balances of all types, including electronic balances, provided their sensitivity is 5 cg or better. Weights presented with such balances fall in this heading, but weights presented separately, even if made of precious metal, are excluded (heading 84.23).
Many of the balances of this heading are designed for precision measurement and are made of non-corrosive metal or of light alloys, with knife-edges, bearings and planes of agate. To protect the balances from air currents and dust, they may be enclosed in a glass or plastics case or built in a cabinet consisting chiefly of glass or plastics; they are then manipulated by handles and other devices outside the cabinet. They may also be fitted with an optical device (e.g., magnifying lens), be artificially illuminated to assist in reading the scale, or be fitted with levelling devices (tripod, adjustable screws, spirit-level, etc.). In certain torsion balances, the weight to be measured is counterbalanced by the torsion of a wire.
Certain electronic balances are used in a vacuum or under controlled pressure, to record the variations in weight of substances submitted to special treatment (heating, cooling, the action of a gas, vacuum treatment, exposure to light, etc.). Weight variations are measured by recording the current passing through a magnetic balancing coil. The heading includes : (1) Analytical balances (e.g., microchemical balances, microbalances, aperiodic analytical balances) used mainly in quantitative chemical analysis. (2) Assay balances, used in the assaying of precious metals. (3) Balances for precious stones, graduated in carats. (4) Chemists' balances, yarn balances, samples balances (used to establish the weight of paper, textile fabrics, etc.). (5) Hydrostatic (or specific gravity) balances, for ascertaining the specific gravity of liquids or solids.
PARTS AND ACCESSORIES
Subject to the provisions of Notes 1 and 2 to this Chapter (see the General Explanatory Note), parts and accessories (including mounted or unmounted agate knife-edges, bearings and planes), identifiable as being suitable for use solely or principally with the balances of this heading are also classified here (for example, beams, trays, cabinets, dials, tripods, swing dampers). Balances of a sensitivity poorer than 5 cg are excluded (heading 84.23).
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