The terms "balance" and "scale" are often used interchangeably, and most of us have a hard time identifying their respective characteristics. In fact, the digital scale supplier even refers to some of their own single products as balances and scales.

    There are technical and practical differences between the two, including what exactly is measured and the types of applications they are used for. However, it remains vague when it comes to naming.

    A balance is an instrument that measures mass (basically the amount of substance in something). Real balances measure mass directly by comparing an unknown mass to a known mass, a process that is not affected by changes in gravity. Such a balance will give the same reading regardless of the position, as gravity will act equally on both sides of the balance.

    A balance measures weight, which is the force acting on a mass equal to the mass of the object times the acceleration due to gravity. Scales cannot measure mass directly because the weighing mechanism and the weight of any given object depend on local gravity. On Earth, the acceleration of gravity can vary by up to 0.5%, with distance from the Earth's core and with latitude.

    From a practical standpoint, gravity is assumed or ignored once the scale is calibrated in its position. Therefore, weight is reported in mass units such as kilograms, even though weight is a measure of force using Newtons. This also allows the use of the term "weight" to refer to both weight and mass, which can be the process of determining both.