Editing Weight (section)

== <span id="Measuring weight"></span>Measuring ==
{{Main|Weighing scale}}
{{redirect|Weigh|other uses|Weigh (disambiguation)}}

[[File:Peso-Valdivia-dsc02545.jpg|thumb|A [[weighbridge]], used for weighing trucks]]

Weight is commonly measured using one of two methods. A [[Weighing scale#Spring scales|spring scale]] or [[Weighing scale#Hydraulic or pneumatic scale|hydraulic or pneumatic scale]] measures local weight, the local [[force]] of [[gravity]] on the object (strictly [[apparent weight|''apparent'' weight force]]). Since the local force of gravity can vary by up to 0.5% at different locations, spring scales will measure slightly different weights for the same object (the same mass) at different locations. To standardize weights, scales are always calibrated to read the weight an object would have at a nominal [[standard gravity]] of 9.80665{{spaces}}m/s<sup>2</sup> (approx. 32.174{{spaces}}ft/s<sup>2</sup>). However, this calibration is done at the factory. When the scale is moved to another location on Earth, the force of gravity will be different, causing a slight error. So to be highly accurate and legal for commerce, [[spring scale]]s must be re-calibrated at the location at which they will be used.

A ''[[Weighing scale#balance|balance]]'' on the other hand, compares the weight of an unknown object in one scale pan to the weight of standard masses in the other, using a [[lever]] mechanism – a lever-balance. The standard masses are often referred to, non-technically, as "weights". Since any variations in gravity will act equally on the unknown and the known weights, a lever-balance will indicate the same value at any location on Earth. Therefore, balance "weights" are usually calibrated and marked in [[mass]] units, so the lever-balance measures mass by comparing the Earth's attraction on the unknown object and standard masses in the scale pans. In the absence of a gravitational field, away from planetary bodies (e.g. space), a lever-balance would not work, but on the Moon, for example, it would give the same reading as on Earth. Some balances are marked in weight units, but since the weights are calibrated at the factory for standard gravity, the balance will measure standard weight, i.e. what the object would weigh at standard gravity, not the actual local force of gravity on the object.

If the actual force of gravity on the object is needed, this can be calculated by multiplying the mass measured by the balance by the acceleration due to gravity – either standard gravity (for everyday work) or the precise local gravity (for precision work). Tables of the gravitational acceleration at different locations can be found on the web.

'''Gross weight''' is a term that is generally found in commerce or trade applications, and refers to the total weight of a product and its packaging. Conversely, '''net weight''' refers to the weight of the product alone, discounting the weight of its container or packaging; and '''[[tare weight]]''' is the weight of the packaging alone.