A weighing scale (usually just "scale" in common usage) is a device using for measuring the weight of an object. These scales are often used to measure the weight of a person, but are also used in science to obtain an approximate mass of an object.
The original form of weighing scale consisted of a beam with a fulcrum at its middle. To determine the mass of the object, a combination of reference weights was hung on one end of the beam while the object of unknown mass was hung on the other end. See balance.
Some weighing scales use a spring with a known spring constant (see Hooke's law) and measure the displacement of the spring by any variety of mechanisms to produce an estimate of the gravitational force applied by the object to the scale's platform.
Weighing scales must be calibrated to zero, and most practical spring scales are accurate chiefly between 10% and 90% of their capacity.
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