There are two primary ways to measure weights. Scales and balances are the two options available. The basic difference in the two is that in a scale, weight is measured by weighing the actual object and in a balance, the object to be measured is compared to a standard defined weight.
Scales calculate weight that is the product of mass into gravity (9.807 m/s2) on the force on a spring, whereas a balance or pair of scales using a balance beam compares masses by balancing the weight due to the mass of an object against the weight of one or more known masses. Some of these can be calibrated to read in units of force (weight) such as newtons instead of units of mass such as kilograms. The balance or pair of scales using a traditional balance beam to compare masses may read correctly for mass even if moved to a place with a different non-zero gravitational field strength. Also, the spring balances that are designed with reading of weight (force) in mind would read correctly for weight in a different non-zero gravitational field strength.
Both scales and balances are useful and effective and are chosen as per the weighing requirement. Scales are of mechanical, spring, pneumatic types. They are available in different varieties and models. Balances too are available in various types and models. The original form of a balance consisted of a beam with a fulcrum at its centre. For highest accuracy, the fulcrum would consist of a sharp V-shaped pivot seated in a shallower V-shaped bearing. To determine the mass of the object, a combination of reference masses was hung on one end of the beam while the object of unknown mass was hung on the other end (see balance and steelyard balance). For high precision work, such as empirical chemistry, the centre-beam balance is still one of the most accurate technologies available, and is commonly used for calibrating test masses.
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