For health, shipping and pricing reasons, knowing the weight of an object is important. Even in the classification of people, police records depend on height and weight to formulate a more accurate description of a how a person appears. Likewise, fruits and vegetables depend on price per mass as do goods being shipped. To measure these quantities, you can either use a weight scale or a balance scale.
Science behind a Spring Scale
A non-digital weight scale, also referred to as a spring scale or bathroom scale, relies on a mass, the known resistance of a spring---in physics, this is called the spring constant, k---and the acceleration of gravity, g, to determine the weight of an object. As your body weight applies an amount of force to a spring, it consequently rotates a gear corresponding to your weight amount. Springs are calibrated to accurately measure a known object's weight prior to installation.
Science behind a Digital Scale
With electric weight scales, springs are replaced by strain gauge technology. That is, as weight applies evenly across the surface of the scale, a load cell provides an electric charge, depending on the mass of the object, and the electrical resistance from the load cell passes to a microchip which converts the analog information into a digital readout on the LCD display.
Science behind a Balance Scale
Balance scales have existed as far back as the first measurements and comparisons of masses of gold and other precious metals anf gems, cattle and other livestock, slaves and coal. Unlike digital and spring scales, balance scales do not depend on gravity, spring tension or electrical resistance in calculating weight. Instead, they compare the mass of an object directly to the known mass of another object. For example, with a doctor's scale, a known weight slides across a level, balancing evenly when the force applied to the level accurately corresponds to the force of the scale. Although this is a comparison of masses and kg, most American doctor and gym scales provide readouts in pounds.
The Different Uses of Scales
Because accuracy is important, doctors rely on balance scales to measure their patients' weights. Unlike spring scales, balance scales measure independently of gravity, which can vary according to your position on Earth, and spring tension, which can weaken with frequent use. Digital scales, however, are becoming more popular, from measuring weights for postage to measuring ingredients for cuisines. Unlike spring and balance scales, digital weight scales are less likely to be misread.
Which Type is the Best?
The type of scale you choose depends on your needs and purpose. For instance, spring scales are the cheapest and most convenient--they do not rely on batteries like digital scales or leveling weights like balance scales. On the other hand, digital scales provide easier, more reliable readings. Yet to reduce the influence of factors like gravity, spring tension or the reliance on electricity, balance scales may be the best type for your weight-measuring needs. The scale you choose is up to you.
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