The History of Scales for Weight
Monitoring personal body weight on a scale is a convenience now taken for granted. Technological advances have increased accuracy and performance, but scales for weight measurement have been used for hundreds of centuries.
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Origins
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A modern balance scale. The oldest and simplest scale was the balance. The balance consisted of two metal pans attached to a lever by arms of equal length. An item of unknown mass in one pan could be compared to an item of known mass in the other pan. There are existing examples of balances from Mesopotamia and Egypt dating to 5000 B.C.
Other Early Models
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The ancient Romans used a steelyard, which was an improvement on the principle of the balance. Instead of a fixed lever, the device was suspended from a hook, allowing for changes in distance between the counterweights and the lever's fulcrum. The lever itself was marked with a graduated scale.
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Measurement
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Although ancient scales worked for purposes of measuring trade and wealth, there was no universal standard for measurement until the metric system was enforced throughout Europe in 1837. Metric weights became the standard calibration for counterweight scales still used at the time.
Advancements
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Richard Salter patented a spring scale in Britain in 1838. The scale is based on the principle of Hooke's Law, that the force required to extend a spring holds a direct proportion to the distance the spring is stretched. These types of scales are still used today to measure heavy commercial loads.
Modern Scales
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The theory behind Salter's spring scale is still used today in digital bathroom and commercial scales. These types of scales use strain-gauge technology, which takes evenly distributed weight and transfers the pressure to a single electronic load cell. The pressure placed on the cell changes electrical resistance and allows calculation of weight in the same manner as weight is determined from a stretched spring.
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References
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