Editing Weighing scale (section)

==Pan balance==
===History===
[[File:El pesado del corazón en el Papiro de Hunefer.jpg|thumb|The Ancient Egyptian ''[[Book of the Dead]]'' depicts a scene in which a scribe's heart is weighed against the [[Maat|feather of truth]].]]
The balance scale is such a simple device that its usage likely far predates the evidence. What has allowed archaeologists to link artifacts to weighing scales are the stones for determining absolute mass. The balance scale itself was probably used to determine relative mass long before absolute mass.<ref name="averyweigh-tronix1947"/>

The oldest attested evidence for the existence of weighing scales dates to the [[Fourth Dynasty of Egypt]], with [[Deben (unit)]] balance weights, from the reign of [[Sneferu]] (c. 2600 BC) excavated, though earlier usage has been proposed.<ref>{{Cite journal |last=Rahmstorf |first=Lorenz |title=In Search of the Earliest Balance Weights, Scales and Weighing Systems from the East Mediterranean, the Near and Middle East |url=https://www.academia.edu/1864503}}</ref> Carved stones bearing marks denoting mass and the Egyptian hieroglyphic symbol for gold have been discovered, which suggests that Egyptian merchants had been using an established system of mass measurement to catalog gold shipments or gold mine yields. Although no actual scales from this era have survived, many sets of weighing stones as well as murals depicting the use of balance scales suggest widespread usage.<ref name="jstor44" />

Examples, dating  {{circa|2400–1800 BC}}, have also been found in the [[Indus Valley civilisation|Indus River valley]]. Uniform, polished stone cubes discovered in early settlements were probably used as mass-setting stones in balance scales. Although the cubes bear no markings, their masses are multiples of a common denominator. The cubes are made of many different kinds of stones with varying densities. Clearly their mass, not their size or other characteristics, was a factor in sculpting these cubes.<ref name="jstor44">{{cite journal|author=Petruso, Karl M|title=Early Weights and Weighing in Egypt and the Indus Valley  |journal=M Bulletin |volume=79|year=1981|pages=44–51|jstor=4171634}}</ref>

In China, the earliest weighing balance excavated was from a tomb of the [[state of Chu]] of the Chinese [[Warring States period]] dating back to the 3rd to 4th century BC in Mount Zuojiagong near [[Changsha]], Hunan. The balance was made of wood and used bronze masses.<ref>{{Cite book |title=Ancient Engineers' Inventions: Precursors of the Present (History of Mechanism and Machine Science) |last1=Rossi |first1=Cesare  |last2=Russo  |first2=Flavio  |last3=Russo  |first3=Ferruccio  |year=2009 |isbn=978-9048122523 |publication-date=May 11, 2009 |page=21|publisher=Springer }}</ref><ref>{{Cite book |title=Reconstruction Designs of Lost Ancient Chinese Machinery |last= Yan |first=Hong-Sen |publisher=Springer |year=2007 |publication-date=November 18, 2007 |pages=53–54}}</ref>

Variations on the balance scale, including devices like the cheap and inaccurate ''bismar'' (unequal-armed scales),<ref>{{cite web|url=http://www.isasc.org/Tutorial/Scale-Types.html |title=ISASC |publisher=ISASC |access-date=2014-02-26}}</ref> began to see common usage by c. 400 BC by many small merchants and their customers. A plethora of scale varieties each boasting advantages and improvements over one another appear throughout recorded history, with such great inventors as Leonardo da Vinci lending a personal hand in their development.<ref name="averyweigh-tronix2">{{cite web|url=http://www.averyweigh-tronix.com/main.aspx?p=1.1.3.4 |title=The History of Weighing |publisher=Averyweigh-tronix.com |date=2012-03-02 |access-date=2014-03-05 |url-status=dead |archive-url=https://web.archive.org/web/20120302145347/http://www.averyweigh-tronix.com/main.aspx?p=1.1.3.4 |archive-date=March 2, 2012 }}</ref>

Even with all the advances in weighing scale design and development, all scales until the seventeenth century AD were variations on the balance scale.  The standardization of the weights used – and ensuring traders used the correct weights – was a considerable preoccupation of governments throughout this time.

<gallery widths="200px" heights="200px" class="center">
File:Archaeological site of Akrotiri - Museum of prehistoric Thera - Santorini - weighing dishes - 01.jpg|Weighing dishes from the island of [[Thera]], [[Minoan civilization]], 2000–1500 BC
File:Lionweights-BM.JPG|[[Assyrian lion weights]] (8th century BC) in the [[British Museum]]
File:Weegschaal (unster) met 2 gewichten in brons, 50 tot 200 NC, vindplaats- Onbekend, collectie Gallo-Romeins Museum Tongeren, GRM 48.jpg|Roman [[steelyard balance]] with two bronze weights, 50–200 AD, [[Gallo-Roman Museum, Tongeren]], Belgium
File:Meister der Jahângîr-Memoiren 001.jpg|Emperor [[Jahangir]] (reigned 1605–1627) weighing his son [[Shah Jahan]] on a weighing scale by artist [[Manohar Das|Manohar]] (AD 1615, Mughal dynasty, India)
</gallery>
The original form of a balance consisted of a beam with a fulcrum at its center. 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 (ability)|balance]] and [[steelyard balance]]). For high precision work, such as empirical chemistry, the center beam balance is still one of the most accurate technologies available, and is commonly used for calibrating test masses.

However, bronze fragments discovered in central Germany and Italy had been used during the [[Bronze Age]] as an early form of currency.<ref>{{cite journal |last1=Ialongo |first1=Nicola |last2=Lago |first2=Giancarlo |title=A small change revolution. Weight systems and the emergence of the first Pan-European money |journal= Journal of Archaeological Science|year=2021 |volume=129 |page=105379 |doi=10.1016/j.jas.2021.105379 |bibcode=2021JArSc.129j5379I |doi-access=free |hdl=11573/1547061 |hdl-access=free }}</ref> In the same time period, merchants had used standard weights of equivalent value between 8 and 10.5 grams from Great Britain to Mesopotamia.<ref>{{cite journal |last1=Ialongo |first1=Nicola |last2=Hermann |first2=Raphael |last3=Rahmstorf |first3=Lorenz |title=Bronze Age weight systems as a measure of market integration in Western Eurasia |journal=PNAS |year=2021 |volume=118 |issue=27 |pages=e2105873118 |doi=10.1073/pnas.2105873118 |pmid=34183401 |pmc=8271817 |bibcode=2021PNAS..11805873I |doi-access=free }}</ref>

===Mechanical balances===
[[File:Alte Dezimalwaage.JPG|thumb|Old decimal balance]]
The '''balance''' (also '''balance scale''', '''beam balance''' and '''laboratory balance''') was the first mass measuring instrument invented.<ref name="averyweigh-tronix1947">{{cite web|url=http://www.averyweigh-tronix.com/download.aspx?did=6249 |title=Download – A Short History to Weighing: AWTX Museum Book |publisher=Averyweigh-tronix.com |access-date=2015-03-05 |url-status=dead |archive-url=https://web.archive.org/web/20120302145357/http://www.averyweigh-tronix.com/download.aspx?did=6249 |archive-date=March 2, 2012 }}</ref> In its traditional form, it consists of a pivoted horizontal [[lever]] with arms of equal length{{spaced ndash}}the [[Beam (structure)|beam]] or [[Tron (Scotland)|tron]] {{spaced ndash}}and a weighing pan<ref>Or "scale", "scalepan" or the obsolete "basin" ([https://books.google.com/books?id=FuAwAAAAIAAJ&pg=PA1069&dq=bason+balance+scale&lr= ''A Practical Dictionary of the English and German Languages'' (1869), p.&nbsp;1069]).</ref> suspended from each arm (hence the plural name "''scales''{{-"}} for a weighing instrument). The unknown mass is placed in one pan and standard masses are added to the other pan until the beam is as close to [[Mechanical equilibrium|equilibrium]] as possible. In precision balances, a more accurate determination of the mass is given by the position of a sliding mass moved along a graduated scale. A [[decimal balance]] uses the lever in which the arm for weights is 10 times longer than the arm for weighted objects, so that much lighter weights may be used to weigh heavy object.<ref>''McGraw-Hill Dictionary of Scientific & Technical Terms''</ref> Similarly a [[centesimal balance]] uses arms in ratio 1:100.
[[File:Balance Scale Working Principle.svg|thumb|left|For a simple pan balance to be in equilibrium, the fulcrum must be offset from the lever arm. When this is the case, the higher arm gains a mechanical advantage over the lower because its horizontal separation from the fulcrum is greater.]]
[[File:Odważniki 2, ubt.jpeg|thumb|left|Two 10-[[Gram|decagram]] masses]]
[[File:Gewichtendoos B.jpg|thumb|left|Masses of 50, 20, 1, 2, 5 and 10 grams]]

Unlike spring-based scales, balances are used for the precision measurement of mass as their accuracy is not affected by variations in the local gravitational field. (On Earth, for example, these can amount to ±0.5% between locations.<ref>{{cite book |last=Hodgeman |first=Charles, Ed. |title=Handbook of Chemistry and Physics, 44th Ed. |publisher=Chemical Rubber Publishing Co. |year=1961 |location=Cleveland, USA }} pp.&nbsp;3480–3485.</ref>) A change in the strength of the gravitational field caused by moving the balance does not change the measured mass, because the [[Moment (physics)|moments of force]] on either side of the center balanced beam are affected equally. A center beam balance will render an accurate measurement of mass at any location experiencing a constant gravity or acceleration.

Very [[Accuracy and precision|precise]] measurements are achieved by ensuring that the balance's [[fulcrum (mechanics)|fulcrum]] is essentially [[friction]]-free (a [[knife]] edge is the traditional solution), by attaching a [[wikt:pointer|pointer]] to the beam which [[Amplifier|amplifies]] any [[Absolute deviation|deviation]] from a balance position; and finally by using the [[lever]] principle, which allows [[fraction (mathematics)|fractional]] masses to be applied by [[Motion (physics)|movement]] of a small mass along the measuring arm of the beam, as described above. For greatest accuracy, there needs to be an allowance for the [[buoyancy]] in air, whose effect depends on the densities of the masses involved.

[[File:Balance scales in China 02.jpg|thumb|Aluminum, mass-produced balance scale ([[steelyard balance]]) sold and used throughout China: the scale can be inverted and held by the larger ring beneath the user's right hand to produce greater leverage for heavier loads ([[Hainan]], [[China]], 2011)]]
[[File:Kubanino sur stratpesilo (Vieno).jpg|thumb|upright|Woman on a public weighing scale, [[Vienna]], [[Austria]], 2016]]

To reduce the need for large reference masses, an off-center beam can be used. A balance with an off-center beam can be almost as accurate as a scale with a center beam, but the off-center beam requires special reference masses and cannot be intrinsically checked for accuracy by simply swapping the contents of the pans as a center-beam balance can. To reduce the need for small graduated reference masses, a sliding weight called a poise can be installed so that it can be positioned along a calibrated scale. A poise adds further intricacies to the calibration procedure, since the exact mass of the poise must be adjusted to the exact lever ratio of the beam.

For greater convenience in placing large and awkward loads, a platform can be ''floated'' on a cantilever beam system which brings the proportional force to a ''noseiron'' bearing; this pulls on a ''stilyard rod'' to transmit the reduced force to a conveniently sized beam.
 
One still sees this design in portable beam balances of 500&nbsp;kg capacity which are commonly used in harsh environments without electricity, as well as in the lighter duty mechanical bathroom scale (which actually uses a spring scale, internally). The additional pivots and bearings all reduce the accuracy and complicate calibration; the float system must be corrected for corner errors before the span is corrected by adjusting the balance beam and poise. <!-- Such systems are typically accurate to at best 1/10,000 of their capacity, unless they are expensively engineered.{{citation needed|date=November 2012}} unnecessary as technical finepoint --->

====Roberval balance====
{{main|Roberval balance}}
[[File:Balance scale IMGP9755.jpg|thumb|left|A [[Roberval balance]]. The pivots of the parallelogram understructure makes it insensitive to load positioning away from center, so improves its accuracy, and ease of use. ]]
In 1669 the Frenchman [[Gilles Personne de Roberval]] presented a new kind of balance scale to the French Academy of Sciences. This scale consisted of a pair of vertical columns separated by a pair of equal-length arms and pivoting in the center of each arm from a central vertical column, creating a parallelogram. From the side of each vertical column a peg extended. To the amazement of observers, no matter where Roberval hung two equal weight along the peg, the scale still balanced.  In this sense, the scale was revolutionary: it evolved into the more-commonly encountered form consisting of two pans placed on vertical column located above the fulcrum and the parallelogram below them. The advantage of the Roberval design is that no matter where equal weights are placed in the pans, the scale will still balance.

Further developments have included a [https://www.besslerwheel.com/forum/download.php?id=14967&order=user_id&sid=e055c056e43d2d7da87d910766c9ff39 "gear balance"] in which the parallelogram is replaced by any odd number of interlocking gears greater than one, with alternating gears of the same size and with the central gear fixed to a stand and the outside gears fixed to pans, as well as the "sprocket gear balance" consisting of a bicycle-type chain looped around an odd number of [[sprocket]]s with the central one fixed and the outermost two free to pivot and attached to a pan.

Because it has more moving joints which add friction, the Roberval balance is consistently less accurate than the traditional beam balance, but for many purposes this is compensated for by its usability.

====Torsion balance====
[[File:DRX-3.jpg|thumb|Torsion balance scale made by Torbal]]
The torsion balance is one of the most mechanically accurate of analog balances. Pharmacy schools still teach how to use torsion balances in the U.S. It utilizes pans like a traditional balance that lie on top of a mechanical chamber which bases measurements on the amount of twisting of a wire or fiber inside the chamber. The scale must still use a calibration weight to compare against, and can weigh objects greater than 120&nbsp;mg and come within a margin of error +/- 7&nbsp;mg. Many microbalances and ultra-microbalances that weigh fractional gram values are torsion balances. A common fiber type is quartz crystal.<ref>{{cite web |url=https://www.grainger.com/know-how/equipment-information/kh-laboratory-balance-scale-types-care-terms |title = Types of Balances and Scales, Common Terms & Care - Grainger KnowHow}}</ref>

===Electronic devices===
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====Microbalance====
{{main|Microbalance}}
A [[microbalance]] (also called an ultramicrobalance, or nanobalance) is an instrument capable of making precise measurements of the mass of objects of relatively small mass: on the order of a million parts of a gram and below.

====Analytical balance====
{{main|Analytical balance}}
[[File:Balance-NaCl-1mol.jpg|thumb|upright|Analytical balance]]
An '''analytical balance''' is a class of balance designed to measure small [[mass]] in the sub-milligram range. The measuring pan of an analytical balance (0.1 [[milligram|mg]] or better)  is inside a transparent enclosure with doors so that [[dust]] does not collect and so any air currents in the room do not affect the balance's operation. This enclosure is often called a draft shield. The use of a mechanically [[vented balance safety enclosure]], which has uniquely designed acrylic airfoils, allows a smooth turbulence-free airflow that prevents balance fluctuation and the measure of mass down to 1&nbsp;μg without fluctuations or loss of product. Also, the sample must be at [[room temperature]] to prevent natural [[convection]] from forming air currents inside the enclosure from causing an error in reading.  Single-pan mechanical substitution balances maintain consistent response throughout the useful capacity, which is achieved by maintaining a constant load on the balance beam and thus the fulcrum by subtracting mass on the same side of the beam to which the sample is added.{{citation needed|date=November 2012}}

Electronic analytical scales measure the force needed to counter the mass being measured rather than using actual masses. As such they must have calibration adjustments made to compensate for gravitational differences.<ref>{{cite web|url=http://www.aandd.jp/support/materials/product_training1_balances.pdf |title=A&D training material|publisher=Sandd.jp |access-date=2014-02-26}}</ref> They use an electromagnet to generate a force to counter the sample being measured and output the result by measuring the force needed to achieve balance. Such a measurement device is called an electromagnetic force restoration sensor.<ref>{{cite web |url=http://archives.sensorsmag.com/articles/0602/27/main.shtml |title=Sensors Mag |publisher=Archives.sensorsmag.com |access-date=2014-02-26 |archive-date=2014-01-06 |archive-url=https://web.archive.org/web/20140106053450/http://archives.sensorsmag.com/articles/0602/27/main.shtml |url-status=dead }}</ref>

====Pendulum balance scales====
Pendulum type scales do not use springs. These designs use pendulums and operate as a balance that is unaffected by differences in gravity. An example of application of this design are scales made by the Toledo Scale Company.<ref>{{cite web|url=http://www.utoledo.edu/library/canaday/findingaids1/MSS-153.pdf |title=Finding Aid : The Toledo Scale Collection |publisher=Utoledo.edu |access-date=2014-02-26}}</ref>

====Programmable scales====
A programmable scale has a [[programmable logic controller]] in it, allowing it to be programmed for various applications such as batching, labeling, filling (with check weight function), [[truck scale]]s, and more.

Another important function is counting, e. g. used to count small parts in larger quantities during the annual stock taking. Counting scales (which can also do just weighing) can range from mg to tonnes.<ref>{{Cite web |date=2021-11-04 |title=Industrial rental scales - Counting scales from 0,006 g to 6 t |url=https://mietwaagen.shop/industrial-scale-rental-hire/ |access-date=2023-02-28 |language=de-DE}}</ref>

===Symbolism===
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[[File:Statue of Justice, Central Criminal Court, London, UK - 20030311.jpg|thumb|upright=0.7|"Lady Justice" holding a 2-pan balance beam scale, and a sword: Statue of Justice, Central Criminal Court, London, UK]]
The [[Scales of Justice (symbol)|scales]] (specifically, a two-pan, beam balance) are one of the traditional symbols of [[justice]], as wielded by statues of [[Lady Justice]]. This corresponds to the use in a metaphor of matters being "held in the balance". It has its origins in ancient Egypt.<ref>{{Cite web |last=Clarke |first=Andrew |date=2023-04-13 |title=The History of Weighing Scales: From Ancient Times to Modern Day |url=https://www.mws.ltd.uk/the-history-of-weighing-scales/ |access-date=2023-07-13 |website=MWS Weighing Solutions |language=en-US}}</ref>

Scales also are widely used as a symbol of finance, commerce, or trade, in which they have played a traditional, vital role since ancient times. For instance, balance scales are depicted in the seal of the [[U.S. Department of the Treasury]] and the [[Federal Trade Commission]].

<gallery>
Seal of the United States Department of the Treasury.svg|Seal of the U.S. Department of the Treasury
Seal of the United States Federal Trade Commission.svg|Seal of the U.S. Federal Trade Commission
</gallery>

Scales are also the symbol for the astrological sign [[Libra (astrology)|Libra]].

Scales (specifically, a two-pan, beam balance in a state of equal balance) are the traditional symbol of [[Pyrrhonism]] indicating the equal balance of arguments used in inducing [[epoche]].<ref>Sarah Bakewell, ''How to Live: Or A Life of Montaigne in One Question and Twenty Attempts at an Answer'' 2011 p 127 {{ISBN|1590514831}}</ref>