A digital scale is a measurement device used to measure the weight or mass of an object or substances. Digital scales are often more compact, durable, and precise than other kinds of scales, such as spring scales or balances, which often wear out and give different readings over time. Digital scales require a power source and may not always be completely accurate, but they are generally quite accurate and consistent even when used over extended periods of time. A digital scale may be used for many different purposes ranging from the measurement of ingredients in the kitchen to the precise measurement of substances in a lab.
Most digital scales make their measurements based on an internal strain gauge. A thin foil piece that conducts electricity and is sensitive to deformation is attached with some adhesive to a flexible surface. When weight is applied to the digital scale, various mechanisms within the digital scale ensure the weight is evenly distributed on the strain gauge. The weight bends the flexible surface, deforming the foil piece, which alters the flow of electrical current. Other mechanisms within the scale are able to interpret the degree of deformation and current change and translate it into a weight or mass.
The sensitivity of a given digital scale may vary greatly based on the purpose for which it's used. Scales that are used to measure people generally do not need to be extremely precise as the difference of a few grams—or even, in some cases, a few pounds—is not extremely significant. Kitchen scales, on the other hand, are often used to measure considerably smaller masses; the difference of a few grams of some ingredients could irreparably damage a meal. Scales used in stores that price items, such as produce, by weight need to be quite accurate, as people pay money based on how much the scale says an object weighs.
The scales used in laboratory settings, particularly those used for chemistry, physics, and medical research, need to be extraordinarily accurate. Problems can result from inaccuracies as small as the mass of a few grains of sand. Chemical reactions often require precise amounts of particular substances to successfully run to completion. A digital scale used for laboratory purposes often includes a glass case around the measurement surface to prevent any changes in measured mass resulting from air currents applying slight pressure to the measurement surface. This often occurs when warm or hot objects or substances are measured as the temperature differences can cause air currents that alter the weight measurements.