Weighing Scale

A weighing scale, or balance, is a device used to measure weight or mass, historically built from two plates suspended at equal distances from a fulcrum so that an object of unknown mass could be balanced against reference weights until the plates leveled. A spring scale instead uses a spring of known stiffness, with the object's weight read from how far the spring stretches under Hooke's law, and later designs can be calibrated to read in force units such as newtons rather than mass units. Scales and balances are used throughout commerce, since a great many products are sold and packaged by mass.