Weighing scale

# Weighing scale

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A weighing scale is a measuring instrument
Measuring instrument
In the physical sciences, quality assurance, and engineering, measurement is the activity of obtaining and comparing physical quantities of real-world objects and events. Established standard objects and events are used as units, and the process of measurement gives a number relating the item...

for determining the weight
Weight
In science and engineering, the weight of an object is the force on the object due to gravity. Its magnitude , often denoted by an italic letter W, is the product of the mass m of the object and the magnitude of the local gravitational acceleration g; thus:...

or mass
Mass
Mass can be defined as a quantitive measure of the resistance an object has to change in its velocity.In physics, mass commonly refers to any of the following three properties of matter, which have been shown experimentally to be equivalent:...

of an object. A spring scale
Spring scale
The spring scale apparatus is simply a spring fixed at one end with a hook to attach an object at the other. It works by Hooke's Law, which states that the force needed to extend a spring is proportional to the distance that spring is extended from its rest position...

measures weight by the distance a spring
Spring (device)
A spring is an elastic object used to store mechanical energy. Springs are usually made out of spring steel. Small springs can be wound from pre-hardened stock, while larger ones are made from annealed steel and hardened after fabrication...

deflects under its load. A balance compares the torque
Torque
Torque, moment or moment of force , is the tendency of a force to rotate an object about an axis, fulcrum, or pivot. Just as a force is a push or a pull, a torque can be thought of as a twist....

on the arm due to the sample weight to the torque
Torque
Torque, moment or moment of force , is the tendency of a force to rotate an object about an axis, fulcrum, or pivot. Just as a force is a push or a pull, a torque can be thought of as a twist....

on the arm due to a standard reference weight using a horizontal lever
Lever
In physics, a lever is a rigid object that is used with an appropriate fulcrum or pivot point to either multiply the mechanical force that can be applied to another object or resistance force , or multiply the distance and speed at which the opposite end of the rigid object travels.This leverage...

. Balances are different from scales, in that a balance measures mass
Mass
Mass can be defined as a quantitive measure of the resistance an object has to change in its velocity.In physics, mass commonly refers to any of the following three properties of matter, which have been shown experimentally to be equivalent:...

(or more specifically gravitational mass), where as a scale measures weight
Weight
In science and engineering, the weight of an object is the force on the object due to gravity. Its magnitude , often denoted by an italic letter W, is the product of the mass m of the object and the magnitude of the local gravitational acceleration g; thus:...

(or more specifically, either the tension or compression force
Force
In physics, a force is any influence that causes an object to undergo a change in speed, a change in direction, or a change in shape. In other words, a force is that which can cause an object with mass to change its velocity , i.e., to accelerate, or which can cause a flexible object to deform...

of constraint provided by the scale). Weighing scales are used in many industrial and commercial applications, and products from feathers to loaded tractor-trailers are sold by weight. Specialized medical scales and bathroom scales are used to measure the body weight of human beings.

## History

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 weight. The balance scale itself was probably used to determine relative weight long before absolute weight.

The oldest evidence for the existence of weighing scales dates to c. 2400-1800 B.C.E. in the Indus River valley (modern-day Pakistan). Uniform, polished stone cubes discovered in early settlements were probably used as weight-setting stones in balance scales. Although the cubes bear no markings, their weights are multiples of a common denominator. The cubes are made of many different kinds of stones with varying densities. Clearly their weight, not their size or other characteristics, was a factor in sculpting these cubes. In Egypt, scales can be traced to around 1878 B.C.E., but their usage probably extends much earlier. Carved stones bearing marks denoting weight and the Egyptian hieroglyphic symbol for gold have been discovered, which suggests that Egyptian merchants had been using an established system of weight measurement to catalog gold shipments and/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.

Variations on the balance scale, including devices like the cheap and inaccurate bismar began to see common usage by c. 400 B.C.E. 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.

Even with all the advances in weighing scale design and development, all scales until the seventeenth century C.E. were variations on the balance scale. Although records dating to the 1600s refer to spring scales for measuring weight, the earliest design for such a device dates to 1770 and credits Richard Salter, an early scale-maker. Spring scales came into common usage in 1840 when R. W. Winfield developed the candlestick scale for use in measuring letters and packages. Postal workers could work more quickly with spring scales than balance scales because they could be read instantaneously and did not have to be carefully balanced with each measurement.

By the 1940s various electronic devices were being attached to these designs to make readings more accurate. These were not true digital scales as the actual measuring of weight still relied on springs and balances. Load cells, small nodes that convert pressure to a digital signal, have their beginnings as early as the late-nineteenth century, but it was not until the late-twentieth century that they became accurate enough for widespread usage.

## Balance

The balance (also balance scale, beam balance and laboratory balance) was the first mass measuring instrument invented. In its traditional form, it consists of a pivoted horizontal lever
Lever
In physics, a lever is a rigid object that is used with an appropriate fulcrum or pivot point to either multiply the mechanical force that can be applied to another object or resistance force , or multiply the distance and speed at which the opposite end of the rigid object travels.This leverage...

of equal length arms, called the beam
Beam (structure)
A beam is a horizontal structural element that is capable of withstanding load primarily by resisting bending. The bending force induced into the material of the beam as a result of the external loads, own weight, span and external reactions to these loads is called a bending moment.- Overview...

, with a weighing pan, also called scale, scalepan, or bason (obsolete), suspended from each arm (which is the origin of the originally plural term "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 equilibrium
Mechanical equilibrium
A standard definition of static equilibrium is:This is a strict definition, and often the term "static equilibrium" is used in a more relaxed manner interchangeably with "mechanical equilibrium", as defined next....

as possible. In precision balances, a slider mass is moved along a graduated scale. The slider position gives a fine correction to the mass value. Although a balance technically compares weights, not masses, the weight
Weight
In science and engineering, the weight of an object is the force on the object due to gravity. Its magnitude , often denoted by an italic letter W, is the product of the mass m of the object and the magnitude of the local gravitational acceleration g; thus:...

of an object is proportional to its mass, and the standard weights used with balances are usually labeled in mass units.

Balances are used for precision mass measurement, because unlike spring scales their accuracy is not affected by differences in the local gravity, which can vary by almost 0.5% at different locations on Earth. A change in the strength of the gravitational field caused by moving the balance will not change the measured mass, because the moments of force
Moment (physics)
In physics, the term moment can refer to many different concepts:*Moment of force is the tendency of a force to twist or rotate an object; see the article torque for details. This is an important, basic concept in engineering and physics. A moment is valued mathematically as the product of the...

on either side of the balance beam are affected equally. In fact, a balance will measure the correct mass even on other planets or moons, or any location that experiences a constant gravity or acceleration.

Very precise
Accuracy and precision
In the fields of science, engineering, industry and statistics, the accuracy of a measurement system is the degree of closeness of measurements of a quantity to that quantity's actual value. The precision of a measurement system, also called reproducibility or repeatability, is the degree to which...

measurements are achieved by ensuring that the balance's fulcrum is essentially friction
Friction
Friction is the force resisting the relative motion of solid surfaces, fluid layers, and/or material elements sliding against each other. There are several types of friction:...

-free (a knife
Knife
A knife is a cutting tool with an exposed cutting edge or blade, hand-held or otherwise, with or without a handle. Knives were used at least two-and-a-half million years ago, as evidenced by the Oldowan tools...

edge is the traditional solution), by attaching a pointer to the beam which amplifies
Amplifier
Generally, an amplifier or simply amp, is a device for increasing the power of a signal.In popular use, the term usually describes an electronic amplifier, in which the input "signal" is usually a voltage or a current. In audio applications, amplifiers drive the loudspeakers used in PA systems to...

any deviation
Absolute deviation
In statistics, the absolute deviation of an element of a data set is the absolute difference between that element and a given point. Typically the point from which the deviation is measured is a measure of central tendency, most often the median or sometimes the mean of the data set.D_i = |x_i-m|...

from a balance position; and finally by using the lever
Lever
In physics, a lever is a rigid object that is used with an appropriate fulcrum or pivot point to either multiply the mechanical force that can be applied to another object or resistance force , or multiply the distance and speed at which the opposite end of the rigid object travels.This leverage...

principle, which allows fraction
Fraction (mathematics)
A fraction represents a part of a whole or, more generally, any number of equal parts. When spoken in everyday English, we specify how many parts of a certain size there are, for example, one-half, five-eighths and three-quarters.A common or "vulgar" fraction, such as 1/2, 5/8, 3/4, etc., consists...

al masses to be applied by movement
Motion (physics)
In physics, motion is a change in position of an object with respect to time. Change in action is the result of an unbalanced force. Motion is typically described in terms of velocity, acceleration, displacement and time . An object's velocity cannot change unless it is acted upon by a force, as...

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
Buoyancy
In physics, buoyancy is a force exerted by a fluid that opposes an object's weight. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid. Thus a column of fluid, or an object submerged in the fluid, experiences greater pressure at the bottom of the...

in air, whose effect depends on the densities of the masses involved.

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
Balance (ability)
In biomechanics, balance is an ability to maintain the center of gravity of a body within the base of support with minimal postural sway. When exercising the ability to balance, one is said to be balancing....

and steelyard balance
Steelyard balance
A steelyard balance or steelyard is a straight-beam balance with arms of unequal length. It incorporates a counterweight which slides along the calibrated longer arm to counterbalance the load and indicate its weight...

). For high precision work, the center beam balance is still one of the most accurate technologies available, and is commonly used for calibrating test weights.

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 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.

Some high-end mechanical balances also use dials (with counterbalancing masses instead of springs), a hybrid design with some of the accuracy advantages of the poise and beam but the convenience of a dial reading. These designs are expensive to produce and have become largely obsolete due to the advent of electronic balances.

### Milligram scale

Milligram scales are typical used for drug dealing, industrial, research, chemical, pharmaceutical, electronics, precious metals, jewelry (commonly sold as "carat scale", "diamond scale", and "jewelry scale"), and educational applications.

### Analytical balance

An analytical balance is used to measure mass
Mass
Mass can be defined as a quantitive measure of the resistance an object has to change in its velocity.In physics, mass commonly refers to any of the following three properties of matter, which have been shown experimentally to be equivalent:...

to a very high degree of precision and accuracy. The measuring pan(s) of a high precision (0.1 mg or better) analytical balance are inside a transparent enclosure with doors so that dust
Dust
Dust consists of particles in the atmosphere that arise from various sources such as soil dust lifted up by wind , volcanic eruptions, and pollution...

does not collect and so any air currents in the room do not affect the balance's operation. The use of a vented balance safety enclosure
Vented balance safety enclosure
Vented balance safety enclosures are used in pharmaceutical, chemical, biological, and toxicological laboratories to provide maximum containment for weighing operations in weighing scales...

, which has uniquely designed acrylic airfoils, allows a smooth turbulence-free airflow that prevents balance fluctuation and the measure of mass down to 1 μg without fluctuations or loss of product. Also, the sample must be at room temperature
Room temperature
-Comfort levels:The American Society of Heating, Refrigerating and Air-Conditioning Engineers has listings for suggested temperatures and air flow rates in different types of buildings and different environmental circumstances. For example, a single office in a building has an occupancy ratio per...

to prevent natural convection
Convection
Convection is the movement of molecules within fluids and rheids. It cannot take place in solids, since neither bulk current flows nor significant diffusion can take place in solids....

from forming air currents inside the enclosure, affecting the measure of mass.

Analytical precision is achieved by maintaining a constant load on the balance beam, by subtracting mass on the same side of the beam to which the sample is added. The final balance is achieved by using a small spring force rather than subtracting fixed masses. This makes calling it an "analytical balance" a misnomer, because it should actually be called an "analytical scale", due to it measuring force
Force
In physics, a force is any influence that causes an object to undergo a change in speed, a change in direction, or a change in shape. In other words, a force is that which can cause an object with mass to change its velocity , i.e., to accelerate, or which can cause a flexible object to deform...

, rather than gravitational mass.

## Spring scale

In a typical spring scale, the spring stretches (as in a hanging scale in the produce department of a grocery store) or compresses (as in a simple bathroom scale) in proportion to how hard the Earth pulls down on the object. It is therefore affected by the local gravity. By Hooke's law
Hooke's law
In mechanics, and physics, Hooke's law of elasticity is an approximation that states that the extension of a spring is in direct proportion with the load applied to it. Many materials obey this law as long as the load does not exceed the material's elastic limit. Materials for which Hooke's law...

, every spring has a proportionality constant that relates how hard it is pulled to how far it stretches. Some weighing scales such as a Jolly balance (named after Philipp von Jolly
Philipp von Jolly
Johann Philipp Gustav von Jolly was a German physicist and mathematician.Born in Mannheim as the son of merchant Louis Jolly and Marie Eleonore Jolly, he studied science in Heidelberg, Vienna and Berlin. After his studies, he was appointed professor of mathematics in Heidelberg in 1839 and in...

who invented the balance about 1874) use a spring
Spring (device)
A spring is an elastic object used to store mechanical energy. Springs are usually made out of spring steel. Small springs can be wound from pre-hardened stock, while larger ones are made from annealed steel and hardened after fabrication...

with a known spring constant (see Hooke's law
Hooke's law
In mechanics, and physics, Hooke's law of elasticity is an approximation that states that the extension of a spring is in direct proportion with the load applied to it. Many materials obey this law as long as the load does not exceed the material's elastic limit. Materials for which Hooke's law...

) and measure the displacement of the spring by any variety of mechanisms to produce an estimate of the gravitational force applied by the object, which can be simply hung from the spring or set on a pivot and bearing platform. Rack and pinion mechanisms are often used to convert the linear spring motion to a dial reading.

Spring scales measure weight
Weight
In science and engineering, the weight of an object is the force on the object due to gravity. Its magnitude , often denoted by an italic letter W, is the product of the mass m of the object and the magnitude of the local gravitational acceleration g; thus:...

, or more precisely, the tension force
Force
In physics, a force is any influence that causes an object to undergo a change in speed, a change in direction, or a change in shape. In other words, a force is that which can cause an object with mass to change its velocity , i.e., to accelerate, or which can cause a flexible object to deform...

of constraint acting on an object, opposing the force of gravity. They are usually calibrated
Calibration
Calibration is a comparison between measurements – one of known magnitude or correctness made or set with one device and another measurement made in as similar a way as possible with a second device....

in units
Units of measurement
A unit of measurement is a definite magnitude of a physical quantity, defined and adopted by convention and/or by law, that is used as a standard for measurement of the same physical quantity. Any other value of the physical quantity can be expressed as a simple multiple of the unit of...

of force such as newtons or pounds-force
Pound-force
The pound force is a unit of force in some systems of measurement including English engineering units and British gravitational units.- Definitions :...

. They have two sources of error that balances do not; the measured weight varies with the strength of the local gravitational force, by as much as 0.5% at different locations on Earth, and the elasticity of the measurement spring can vary slightly with temperature. Spring scales which are legal for commerce either have temperature compensated springs or are used at a fairly constant temperature, and must be calibrated at the location in which they are used, to eliminate the effect of gravity variations.

## Strain gauge scale

In electronic versions of spring scales, the deflection of a beam supporting the unknown weight is measured using a strain gauge
Strain gauge
A strain gauge is a device used to measure the strain of an object. Invented by Edward E. Simmons and Arthur C. Ruge in 1938, the most common type of strain gauge consists of an insulating flexible backing which supports a metallic foil pattern. The gauge is attached to the object by a suitable...

, which is a length-sensitive electrical resistance
Electrical resistance
The electrical resistance of an electrical element is the opposition to the passage of an electric current through that element; the inverse quantity is electrical conductance, the ease at which an electric current passes. Electrical resistance shares some conceptual parallels with the mechanical...

. The capacity of such devices is only limited by the resistance of the beam to deflection. The results from several supporting locations may be added electronically, so this technique is suitable for determining the weight of very heavy objects, such as trucks and rail cars, and is used in a modern weighbridge.

## Hydraulic or pneumatic scale

It is also common in high-capacity applications such as crane scales to use hydraulic force to sense weight. The test force is applied to a piston or diaphragm and transmitted through hydraulic lines to a dial indicator based on a Bourdon tube or electronic sensor.

## Testing and certification

Most countries regulate the design and servicing of scales used for commerce. This has tended to cause scale technology to lag behind other technologies because expensive regulatory hurdles are involved in introducing new designs. Nevertheless, there has been a recent trend to "digital load cells" which are actually strain-gauge cells with dedicated analog converters and networking built into the cell itself. Such designs have reduced the service problems inherent with combining and transmitting a number of 20 millivolt signals in hostile environments.

Government regulation generally requires periodic inspections by licensed technicians using weights whose calibration is traceable to an approved laboratory. Scales intended for casual use such as bathroom or diet scales may be produced, but must by law be labelled "Not Legal for Trade" to ensure that they are not repurposed in a way that jeopardizes commercial interest. In the United States, the document describing how scales must be designed, installed, and used for commercial purposes is NIST
National Institute of Standards and Technology
The National Institute of Standards and Technology , known between 1901 and 1988 as the National Bureau of Standards , is a measurement standards laboratory, otherwise known as a National Metrological Institute , which is a non-regulatory agency of the United States Department of Commerce...

Handbook 44.
Legal For Trade certification usually approve the readability as repeatability/10 to ensure a maximum margin of error of 10%.

Because gravity varies by over 0.5% over the surface of the earth, the distinction between force due to gravity and mass is relevant for accurate calibration of scales for commercial purposes. Usually the goal is to measure the mass of the sample rather than its force due to gravity at that particular location.

Traditional mechanical balance-beam scales intrinsically measured mass
Mass
Mass can be defined as a quantitive measure of the resistance an object has to change in its velocity.In physics, mass commonly refers to any of the following three properties of matter, which have been shown experimentally to be equivalent:...

. But ordinary electronic scales intrinsically measure the gravitational force between the sample and the earth, i.e. the weight
Weight
In science and engineering, the weight of an object is the force on the object due to gravity. Its magnitude , often denoted by an italic letter W, is the product of the mass m of the object and the magnitude of the local gravitational acceleration g; thus:...

of the sample, which varies with location. So such a scale has to be re-calibrated after installation, for that specific location, in order to obtain an accurate indication of mass.

See Verification and validation
Verification and Validation
In software project management, software testing, and software engineering, verification and validation is the process of checking that a software system meets specifications and that it fulfills its intended purpose...

for further information

## Supermarket/retail scale

These scales are used in the bakery
Bakery
A bakery is an establishment which produces and sells flour-based food baked in an oven such as bread, cakes, pastries and pies. Some retail bakeries are also cafés, serving coffee and tea to customers who wish to consume the baked goods on the premises.-See also:*Baker*Cake...

, delicatessen
Delicatessen
Delicatessen is a term meaning "delicacies" or "fine foods". The word entered English via German,with the old German spelling , plural of Delikatesse "delicacy", ultimately from Latin delicatus....

, seafood
Seafood
Seafood is any form of marine life regarded as food by humans. Seafoods include fish, molluscs , crustaceans , echinoderms . Edible sea plants, such as some seaweeds and microalgae, are also seafood, and are widely eaten around the world, especially in Asia...

, meat
Meat
Meat is animal flesh that is used as food. Most often, this means the skeletal muscle and associated fat and other tissues, but it may also describe other edible tissues such as organs and offal...

, produce
Produce
Produce is a generalized term for a group of farm-produced goods and, not limited to fruits and vegetables . More specifically, the term "produce" often implies that the products are fresh and generally in the same state as where they were harvested. In supermarkets the term is also used to refer...

, and other perishable departments. Supermarket scales can print labels and receipts (in bakery
Bakery
A bakery is an establishment which produces and sells flour-based food baked in an oven such as bread, cakes, pastries and pies. Some retail bakeries are also cafés, serving coffee and tea to customers who wish to consume the baked goods on the premises.-See also:*Baker*Cake...

specially), marks weight/count, unit price, total price and in some cases tare, a supermarket label prints weight/count, unit price and total price. Some modern supermarket scales print an RFID tag that can be used to track the item for tampering or returns. In most cases these type of scales have a sealed calibration so that the reading on the display is correct and cannot be tampered with - in the USA the approval is NTEP, for South Africa it is SABS, the UK it is OIML.

## Sources of error

Some of the sources of error
Errors and residuals in statistics
In statistics and optimization, statistical errors and residuals are two closely related and easily confused measures of the deviation of a sample from its "theoretical value"...

in high-precision balances or scales are:
• Buoyancy
Buoyancy
In physics, buoyancy is a force exerted by a fluid that opposes an object's weight. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid. Thus a column of fluid, or an object submerged in the fluid, experiences greater pressure at the bottom of the...

, because the object being weighed displaces a certain amount of air, which must be accounted for. Some high-precision balances may be operated in a vacuum.
• Error in mass of reference weight
• Air gusts, even small ones, which push the scale up or down
• Friction
Friction
Friction is the force resisting the relative motion of solid surfaces, fluid layers, and/or material elements sliding against each other. There are several types of friction:...

in the moving components that cause the scale to reach equilibrium at a different configuration than a frictionless equilibrium should occur.
• Settling airborne dust contributing to the weight
• Mis-calibration over time, due to drift in the circuit's accuracy, or temperature change
• Mis-aligned mechanical components due to thermal expansion
Thermal expansion
Thermal expansion is the tendency of matter to change in volume in response to a change in temperature.When a substance is heated, its particles begin moving more and thus usually maintain a greater average separation. Materials which contract with increasing temperature are rare; this effect is...

/contraction of components
• Magnetic fields acting on ferrous components
• Forces from electrostatic fields, for example, from feet shuffled on carpets on a dry day
• Chemical reactivity between air and the substance being weighed (or the balance itself, in the form of corrosion
Corrosion
Corrosion is the disintegration of an engineered material into its constituent atoms due to chemical reactions with its surroundings. In the most common use of the word, this means electrochemical oxidation of metals in reaction with an oxidant such as oxygen...

)
• Condensation
Condensation
Condensation is the change of the physical state of matter from gaseous phase into liquid phase, and is the reverse of vaporization. When the transition happens from the gaseous phase into the solid phase directly, the change is called deposition....

of atmospheric water on cold items
• Evaporation
Evaporation
Evaporation is a type of vaporization of a liquid that occurs only on the surface of a liquid. The other type of vaporization is boiling, which, instead, occurs on the entire mass of the liquid....

of water from wet items
• Convection
Convection
Convection is the movement of molecules within fluids and rheids. It cannot take place in solids, since neither bulk current flows nor significant diffusion can take place in solids....

of air from hot or cold items
• Gravitational anomalies for a scale, but not for a balance. I.e. using the scale near a mountain; failing to level and recalibrate the scale after moving it from one geographical location to another)
• Vibration and seismic disturbances; for example, the rumbling from a passing truck
• cables used for connecting the main machine to the display may damage due to heavy weights.

## Software

An ongoing problem within the free software
Free software
Free software, software libre or libre software is software that can be used, studied, and modified without restriction, and which can be copied and redistributed in modified or unmodified form either without restriction, or with restrictions that only ensure that further recipients can also do...

community is the lack of free software for analytical balances which is currently debated by some manufacturers.

## Symbolism

The scales (specifically, a two pan, beam balance) are one of the traditional symbols of justice
Justice
Justice is a concept of moral rightness based on ethics, rationality, law, natural law, religion, or equity, along with the punishment of the breach of said ethics; justice is the act of being just and/or fair.-Concept of justice:...

, as wielded by statues of Lady Justice
Lady Justice |Dike]]) is an allegorical personification of the moral force in judicial systems.-Depiction:The personification of justice balancing the scales of truth and fairness dates back to the Goddess Maat, and later Isis, of ancient Egypt. The Hellenic deities Themis and Dike were later...

. This corresponds to the use in metaphor of matters being "held in the balance". It has its origins in ancient Egypt.

Scales are also the symbol for the astrological sign Libra
Libra (astrology)
Libra is the seventh astrological sign in the Zodiac, originating from the constellation of Libra. In astrology, Libra is considered a "masculine", positive sign. It is also considered an air sign and is one of four cardinal signs...

.

• Ampere balance
Ampere balance
The ampere balance is an electromechanical apparatus used for the precise measurement of the SI unit of electric current, the ampere. It was invented by William Thomson, 1st Baron Kelvin....

• Apparent weight
Apparent weight
The weight in a given frame of reference is a generalized concept of weight, see the ISO definition of weight.An object's regular weight is its weight with respect to Earth...

• AutoAnalyzer
AutoAnalyzer
AutoAnalyzer is an automated analyzer using a special flow technique named "continuous flow analysis " first made by the Technicon Corporation. The instrument was invented 1957 by Leonard Skeggs, PhD and commercialized by Jack Whitehead's Technicon Corporation...

• Libra
Libra (astrology)
Libra is the seventh astrological sign in the Zodiac, originating from the constellation of Libra. In astrology, Libra is considered a "masculine", positive sign. It is also considered an air sign and is one of four cardinal signs...

• Mass versus weight
Mass versus weight
In everyday usage, the mass of an object is often referred to as its weight though these are in fact different concepts and quantities. In scientific contexts, mass refers loosely to the amount of "matter" in an object , whereas weight refers to the force experienced by an object due to gravity...

A multihead weigher is a fast, accurate and reliable weighing machine, used in packing both food and non-food products.-History:The multihead weigher was first invented and brought to market by Ishida, back in the early 1970s as a solution to quickly distributing vegetables of varying weight to...

• Combination weigher
• Nutrition scale
Nutrition scale
A Nutrition scale is a weighing instrument that output precise nutritional information for foods or liquids. Most scales calculate calories, carbohydrates, and fats, with more sophisticated scales calculating additional nutrients such as Vitamin K, potassium, magnesium, and sodium.Scales often use...

• Roberval Balance
Roberval Balance
The Roberval Balance is a weighing scale presented to the French Academy of Sciences by the French mathematician Gilles Personne de Roberval in 1669....

• Steelyard balance
Steelyard balance
A steelyard balance or steelyard is a straight-beam balance with arms of unequal length. It incorporates a counterweight which slides along the calibrated longer arm to counterbalance the load and indicate its weight...

• Tare weight
Tare weight
Tare , from the Middle French word tare "wastage in goods, deficiency, imperfection" , from Italian tara, from Arabic tarah, lit. "thing deducted or rejected," from taraha "to reject" weight, sometimes called unladen weight, is the weight of an empty vehicle or container...

• Watt balance
Watt balance
The watt balance is an experimental electromechanical weight measuring instrument that measures the weight of a test object very precisely by the strength of an electric current and a voltage. It is being developed as a metrological instrument that may one day provide a definition of the kilogram...

• Weigh house - historic public building for the weighing of goods
• Weigh lock
Weigh lock
A weigh lock is a specialized canal lock designed to determine the weight of barges in order to assess toll payments based upon the weight and value of the cargo carried. This requires that the unladen weight of the barge be known....

- for weighing canal barges
• Weighbridge - for weighing vehicles (such as trucks) and railcars