# Dictionary of Laboratory Terms/AZ
## A
### Accreditation

    Formal recognition of the technical and organizational competence of a calibration, testing, inspection or certification laboratory to perform a specific service within the scope of the accreditation according to internationally governing standards. In many cases, accreditation is according to ISO 17025 "General requirements for the competence of testing and calibration laboratories".

### Accuracy

    1. Closeness of agreement between a measured quantity value and a true quantity value of a measurand ([VIM:2012]).
    2. Qualitative designation for the closeness of the approximation of determined results to the reference value. The reference value may be defined or agreed to be the true value of the expected value.
    3. The closeness of the agreement between a test result and the accepted reference value. Example: ability of a measuring instrument to deliver output quantities that are close to the true value. For repeated measurements, accuracy requires trueness (absence of systematic errors) and precision. For a single measurement, this need not necessarily be the case.
    4. The property of the stated values of a reference material to correspond to their true value.

### Adjust, to

    1. Set of operations carried out on a measuring system so that it provides prescribed indications corresponding to given values of a quantity to be measured([VIM:2012]).
    2. Adjusting is the action of setting a measuring instrument or standard so that the measured value is correct, or deviates as little as possible from the correct value, or the deviation remains within acceptable limits of error. This is obtained in the case of a measuring instrument, through adjusting the manual fine settings of its indication by trained specialist personnel, or semi- or automatically by the user, if the instrument has an adjusting mechanism (self-adjustment).

### Adjustment

    Result of the action of adjusting (to adjust) an instrument.

### Air humidity

    The amount of water vapor in the air. Relative humidity h is the ratio between the actual vapor pressure of water and its saturated vapor pressure.

### Air pressure

    The static pressure prevailing in the mixture of gases that forms the Earth's atmosphere. Mean air pressure at sea level is 1013 hPa (normal pressure) and decreases continuously with increasing height. It also fluctuates constantly with changing weather conditions. The standard deviation of these fluctuations from the local mean value over a period of two or more weeks at temperate latitudes is of the order of 7 hPa, or approximately 0.7% of normal pressure.
    In meteorology, the local air pressure is referred to as "station pressure", which is abbreviated to STP or QFE. On weather charts, however, the air pressure reduced to sea level is shown, which is indicated by the abbreviation SLP (sea level pressure) or QFF. If the density of air is to be determined for the correction for air buoyancy, station pressure (STP or QFE) must be used.

### Ambient temperature

    Temperature of the air surrounding the instrument and the measurand.

### Analog data processing device

    Electronic device in an instrument that performs the analog-digital conversion of the output signal, performs further processing of these data, and forwards the results in digital form across an interface, but without indicating them.

### Analog signal

    A stepless variable, usually electrical quantity (e.g. current, voltage, resistance) that is proportional to the measurement value.

### Analog-digital converter

    An electronic device for converting analog signals (current, voltage, resistance) into digital signals, e.g. in a digital voltmeter. Often referred to as A/D converter.

### Analytical balance

    1.Collective term for weighing instrument of special accuracy with high resolution of accuracy class I. Analytical balances are subdivided into microanalytical-, semimicro-, micro- and ultramicro balances. Although the weighing capacity and readability of these balances were originally selected to be suitable for chemical analyses, such balances are used wherever there is a requirement for high resolution and accuracy. On an analytical balance a small quantity can be weighed in a relatively heavy container, which requires a readability of 0.1 mg or less and at least 100000 actual scale intervals. Because of their high resolution (i.e. small readability), analytical balances are fitted with a draft sheld to protect them from disturbing air currents.
    2. Strictly by definition: weighing instrument of accuracy class I with a weighing capacity in the range of 100-400 g (typically 200 g) and a readability of 0.1 mg. Also referred to as microanalytical balance.
    3. Strictly by definition: weighing instrument according to 2. that satisfies the corresponding legal metrology requirements.

### Application range of a weighing instrument

    Restrictions regarding the intended use and/or environmental conditions under which a laboratory instrument may be used. E.g.: temeperature limits -10 to 40 °C.

### Areometer

    Synonym for "hydrometer".

### ASTM International

    An organization in the United States of America that develops standards as well as related technical information and services that are globally recognized. The organization was formerly known as the American Society for Testing and Materials (ASTM).

### ATEX

    Abbreviation for the French term "atmosphère explosible" (explosive atmosphere) ([94/9/EC, 1999/92/EC]).

### ATEX 137 directive

    This European Directive regulates the organizational and technical measures for the operators of plants to ensure that in hazardous areas there is no safety risk from explosions for persons working in those areas.
    The operator of a plant must prepare a risk analysis of potential explosion hazards and specify measures to reduce the hazards to an acceptable level (explosion protection document). Equipment, components, and protective systems intended for use in hazardous areas must be installed, operated, and maintained appropriately and according to the manufacturer's instructions. The directive is implemented as national law in the EU. Each country is entitled to define further measures.

### ATEX 95 directive

    This European directive regulates the measures to ensure that equipment, components, and protective systems that are intended for use in hazardous areas may only be put into operation and installed provided that, with appropriate installation and maintenance, they do not present a hazard to people. In addition, the manufacturer must ensure that the affected installations comply with the so-called "essential health and safety requirements" that are listed in the directive. The directive is implemented as national law in the EU.

### Automatic adjustment

    Device for automatic adjustment of a laboratory instrument. The adjustment operation can be performed, for instance, by pressing a button, or automatically after a certain period of time, or by a change of temperature.

## B
### Back-weighing

    (Re)weighing of a sample after a chemical or thermal reaction, or physical process, that changes the mass of the sample.

### Balance

    Weighing instrument, intended predominantly for medium to low capacity weighments, with moderate to high resolutions, mostly used indoors, often in laboratory environments and typically of OIML class I or II.

### Bar code

In a bar code, numeric and alphanumeric characters are represented as combinations of bars and spaces of different width. The width and separation of the bars represent the coding, which can be read and evaluated with corresponding bar code readers. Different types of code have been developed for different applications. For prepackages, these are the UPC Code (Universal Product Code, in the USA and Canada) and the EAN code in Europe and many countries overseas.

### Bias

    1. The difference between the expectation (statistical expectation, i.e. the average of several results) of the test results of an accepted reference value and that reference value.
    2. Estimate of the systematic measurement error ([VIM:2012]).

### BIML

    Abbreviation for "Bureau International de Métrologie Légale", the International Bureau of Legal Metrology. The headquarters offices of the BIML are in Paris. Its responsibilities include the management and organization of the OIML, the preparation of OIML recommendations and documents, and the convening of meetings, for example to approve such items.

### BIPM

    Abbreviation for the "Bureau International des Poids et Mesures", the International Bureau of Weights and Measures, which has its headquarters in Sèvres, a suburb of Paris. The task of the BIPM is to ensure worldwide uniformity of measurements and their traceability to the International System of Units (SI). The BIPM was founded for this purpose within the context of the Meter Convention, and operates under the supervision of the International Committee for Weights and Measures.

### Buoyancy

    A force that acts on any body that is immersed in a fluid and acts against gravity, thereby causing an effective reduction in weight. According to Archimedes’ principle, the buoyancy force $F_{B}$ is equal to the weight force of the displaced fluid.
    $F_{B}=m_{F}g=(d_{F}V)g$
    where $m_{F}$ mass of the displaced fluid, $g$ local gravity, $d_{F}$ density of the fluid, $V$ volume of the body.

### Burette

    A burette is a glass tube marked with a scale that has a tap at its lower end and is used to dispense known amounts of liquid, mainly for titration. The volume (volumetry) that has been dispensed can be read off the scale. There are also burettes that are integrated into a titration apparatus with supply bottle. A further version consists of a bottle-mounting instrument with a piston-cylinder system. An advantage of this version is the digitally readable volume.

## C
### Calibrate, to

    1. Action of establishing a relation between the quantity values provided by measurement standards and corresponding indications ([VIM:2012]).
    2. Action of determining the deviation between the measurement value and the true value of the measurand under specific measurement conditions without making any changes.
    3. Term used in technical language for "to adjust" especially for pH sensors.

### Calibration

    Result of the action of calibrating an instrument.

### Calibration laboratory meeting ISO 17025

    Testing or calibration laboratory accredited to ISO/IEC 17025. The accreditation confirms that the laboratory possesses the competence to perform tests and/or calibrations according to the requirements of ISO/IEC 17025.

### Calibration service

    Organization for the accreditation and monitoring of calibration laboratories in industrial and other institutions (e.g. technical inspection authorities, university institutes, national authorities) with the aim of ensuring the traceability of measuring equipment and standards to national standards, particularly in industrial metrology.

### CE mark

    By affixing the CE mark, the manufacturer declares that the marked instrument conforms to all applicable European Directives. For laboratory instruments, these are the Low Voltage Directive 2006/95/EC, EMC Directive 2004/108/EC and Measuring Instruments Directive 2004/22/EC (where applicable). In addition to the CE mark on the instrument, the manufacturer issues an Declaration of Conformity, in which conformity with all applicable European Directives is explicitly confirmed.

### Certificate of conformity

    The conformance of verified laboratory instruments to the European directive (EC) type approval is documented by the verification authority by issuing a certificate of conformity at the time of verification.

### Characteristic curve

    The relationship between the input variable and the output variable of a measuring instrument. The characteristic curve is obtained by recording, and usually displaying graphically, the output values for possible values of the input range.

### CIPM

    Abbreviation for "Comité International des poids et mesures", the International Committee for Weights and Measures. The CIPM is made up of eighteen individuals, each from a different Member State under the Metre Convention. Its principal task is to promote world-wide uniformity in units of measurement (International System of Units, SI) by direct action or by submitting draft resolutions to the General Conference (CGPM, General Conference on Weights and Measures).

### Combined error

    A measurement deviation that is composed of several random or systematic components. Known systematic measurement deviations (systematic error) must be taken into account (correction). All other components (random errors and measurement uncertainty of the systematic errors) are considered to be random quantities when the measurement uncertainty is determined.

### Compulsory verification

    According to the Weights and Measures Act, this obligation exists for certain instruments if they are used in commercial and official activities, in the field of public health, or in the preparation and testing of pharmaceutical products.

### Confidence level

    Probability that the expected value of a measurand lies within the (usually symmetrical) coverage interval ±U of the measurement value. For a given coverage interval, the confidence level depends on the probability distribution of the measurement value.

### Constructional requirements

    Legal regulations, guidelines, or standards that apply to laboratory instruments.

### Control chart

    In the control chart, values that were obtained from repeated sample checks of a process are entered, usually graphically. The control chart is used to monitor the process. Should a sample value attain the warning limit or control limit, the process must be corrected if necessary.

### Control limit

    Tolerance of a process relative to its target value. Violation of the tolerance is an infringement of the quality requirements, and therefore requires a correction of the process.

### Control unit

    Electronic device in a laboratory instrument that performs the analog-digital conversion of the output signal, as well as further processing of these data including display of the results.

### Converter

    Device that converts quantities of one medium into quantities of another medium, the converter creating a relationship between the quantities (usually proportionality). Media can be, for example, physical or numerical quantities. Examples of converters are the electrodynamic converter and the analog-digital converter.

### Coverage interval

    Range U (uncertainty interval) on both sides of a measurement value (corrected for systematic error) that contains the expected value of the measurand with a specified confidence level. Assuming that the underlying quantity is normally distributed, the confidence level for k = 1 (expansion factor) is approximately 68%, for k = 2 approximately 95%, and for k = 3 approximately 99.7%.

### Creep error

    The deviation that arises when a drifting measurement value is read, printed, or processed before the gradual approach to the stable state (e.g. of the measurement value) has been completed (settling).

## D
### Damping

    Reduction of the amplitude of a periodically varying quantity. In the case of a laboratory instrument, the reduction in amplitude of oscillations until a stable equilibrium is reached (settling). The oscillation energy is directly dissipated, e.g. as frictional heat or electrical heat, or transformed into a different form (e.g. electrical energy in the case of electrodynamically compensating measuring instruments).

### Data matrix code

    Representation of numeric and alphanumeric characters by means of a pattern of square dots in a square surface. A square with a relatively small number of subdivisions can already encode an enormous amount of data. For example, a 10 x 10 matrix code can encode $2^{100}\approx 10^{30}$ bits of data. This allows sufficient redundancy to correct any errors that may occur.

### Data plate

    Plate on which the designations and inscriptions stipulated in the verification, safety, and other regulations are all
displayed.
    1. Plate containing information for a more detailed identification of the respective product, for example, name of the manufacturer, model, serial number, maximum capacity, operating voltage, power supply frequency, type data, approval data, instructions regarding intended use, safety instructions, etc. The required inscriptions are defined more specifically in the applicable legal regulations for the respective instrument.
    2. More specifically, the term "marking" is used for the CE mark (CE marking), while the remaining items of information on the plate are referred to as "inscriptions". In non-technical language, the terms "name plate" and "type plate" are also used synonymously for "data plate".

### Degree of protection (IP) provided by enclosures

    Characteristics defined in standards relating to equipment safety, a.k.a. "ingress protection". IEC 60529 is concerned with the protection of electrical equipment by housings, covers, and the like. The standard concerns the protection of persons against contact with electrically live or moving parts, the protection of equipment against the ingress of solid objects and water, and defines the codes for internationally agreed types and levels of protection (IP Code). The first digit of the IP Code defines the level of protection against contact and the ingress of solid objects, the second digit defines the level of protection against ingress by water.
Levels of IP protection: 1st and 2nd digits. :
| First digit | Protection against contact and ingress of solid objects | Second digit | Protection against water |
| 0 | non-protected | 0 | non-protected |
| 1 | $\geq$ 50 mm diameter | 1 | vertically dripping |
| 2 | $\geq$ 12.5 mm diameter | 2 | dripping (15° tilted) |
| 3 | $\geq$ 2.5 mm diameter | 3 | spraying |
| 4 | $\geq$ 1.0 mm diameter | 4 | splashing |
| 5 | dust-protected | 5 | jetting |
| 6 | dust-tight | 6 | powerful jetting |
| - | - | 7 | temporary immersion |
| - | - | 8 | continuous immersion |

### Densitometer

    A measuring instrument to determine the density of fluids.

### Density

    The density $d$ of a body is the ration of its mass $m$ to its volume $V$.
    $d={\frac {m}{V}}$

### Design qualification

    Part of Equipment Qualification (EQ). The Design Qualification defines the specifications of the instrument and documents the decision process that results in selection of the supplier and of the instrument.

### Deviation

    1. Deviation of a value obtained by measurement, and assigned to the measurand, from the true value.
    2. Value minus its reference value (measurement deviation).

### Differential weighing

    1. A change (increase or decrease) in mass that is determined by two successive weighments, usually of the same object, to which between the weighments a change was made, and wherever possible with the same balance and same tare weight.
    2. Comparison of mass of a weighed object with a mass standard (reference normal).

### Digit

    The smallest indicated scale interval on a laboratory instruments that have a digital display.

### Digital display

    In contrast to an analog readout, a readout or printout exclusively in the form of numbers, the last digit being rounded. A digital display or digital printout is unambiguously readable and the transfer of measurement values to data processing systems is possible by very simple means, but a digital value cannot be interpolated without additional information and it is difficult to deduce the dynamics of changing values e.g. during settling.

### Digital filter

    A signal filter that is implemented with a digital algorithm. A computer uses filter coefficients to form the output value from the current and past input values in real time. Digital filters can suppress low-frequency (e.g. ~10 Hz) signal components in the measured signal that are caused by, for instance, air currents, vibrations in the foundations, or noise of electronic components. Suppression of these components stabilizes the displayed measurement value.
    An example of a simple digital filter is one that calculates the arithmetic mean of all incoming values over a specified period of time.

### Digital interval

    Difference between two successive digits of equal significance.

### Digital-analog converter

    An electronic device for converting digital signals into analog signals (voltages, currents, resistances). Often referred to as D/A converter. Is used, for example, to plot the progress of a change in weight in analog form with a line plotter.

### Directive on Electromagnetic Compatibility

    European Directive for instruments that may cause electromagnetic interference, or whose operation may be impaired by such interference. It stipulates the requirements for protection in this area as well as the corresponding control modalities.
    The EMC directive is implemented as national law in Europe.

### Dispensing

    Separating a quantity into a number of partial quantities within defined tolerance limits.

### Display

    Element of an instrument serving to represent figures, letters, and/or other information.

### Division

    All the divisions of a lined scale or all the numbers of a numeric scale.

### Drift

    The slow change over time in the value of a metrological characteristic (indication) of a measuring instrument under constant or stationary conditions.
    For example, a slowly changing temperature is referred to as temperature drift.

### Dry content

    The proportion of solid materials contained in a mixture of solids and lilquids, expressed in percent of the total mass of the mixture.

### Drying oven method

    Method for determining the moisture content of a sample, in which the sample is dried in a drying oven at a constant temperature for a defined period of time. The difference in weight before and after drying is used to calculate the moisture content as a percentage.

## E
### EAN

    Abbreviation for "European Article Numbering". This numbering system allows products to be uniquely identified internationally by a 13-digit number. In the form of a bar code, this number is in commercial use for inventory control.

### EDQM

    European Directorate for the Quality of Medicines.

### Electric charge

    Physical quantity which, among other things, is the source of the electric field and of force effects. The electric charge can be positive or negative (polarity); charges with opposite polarity attract, those with the same polarity repel.

### Electrical safety

    Non-technical term for the requirements of the Low Voltage Directive.

### Electromagnetic compatibility (EMC)

    The ability of an electrical apparatus, device, or system to function satisfactorily (i.e., comply with the error limits) within its electromagnetic environment without itself causing electromagnetic interference that would be unacceptable for all apparatuses, equipment, or systems in this environment.
    In the European Union, the requirements for instruments are regulated by the European Directive on Electromagnetic Compatibility ([2004/108/EC]).

### Electromagnetic force compensation

    Weighing principle in which the weight force of the weighed object is opposed by a force of equal magnitude that is produced with the aid of an electrodynamic converter. An electronic control system that responds to the displacement of the load cell (position sensor) causes the compensation current to be adjusted so that a disequilibrium of the forces arising from loading or unloading is restored to equilibrium. The weight force is proportional to the mass of the weighed object and in the stable state is completely compensated by the electrodynamically generated force. This force is itself proportional to the electric current flowing in the converter. The current is thus proportional to the mass placed on the balance and can therefore by used as a measurement signal.

### Electrostatic charging

    Electric charge that many accumulate on objects (solids, liquids, or gases) that have low electrical conductivity (so-called electric insulators) such as glass, plastic, organic solvents, seeds, powders, dusts, etc.

### Electrostatic discharging

    When electrostatically charged people or objects touch parts of a weighing instrument, an instantaneous electrostatic discharge can occur (discharge voltage several kilovolts, energy several millijoules). This causes a momentary discharge current to flow through the instrument that has an order of magnitude of several kiloamperes and which can adversely affect the correctness of the measurement value determination or even destroy electronic circuits.

### Endurance of the printout

    Certification requirements exist for the printout of weighing results, e.g. printouts for the intended purpose must be clear and enduring, i.e. good readability must be assured for a minimum of a) two years under the usual archiving obligations; b) one month for price-mark devices and industrial scales; c) one week for scales for public points of sale even under adverse conditions (contact with grease or food, effect of light).

### Environmental influence

    External circumstances that may adversely affect the metrological behavior of a laboratory instrument. These may include, for example, setting up, ambient temperature, air current, weather conditions, magnetic fields, electrostatic forces, and vibrations.

### Equipment Qualification

    Officially undefined but commonly used term in instrument qualification. Qualification is the process that proves and documents that an instrument functions correctly and delivers the expected results (EU Guide on Manufacture).
    Equipment Qualification (EQ) contains the following qualification steps: Design Qualification (DQ), Installation Qualification (IQ), Operational Qualification (OQ), Performance Qualification (PQ) and Maintenance Qualification (MQ).

### Error limits

    Maximum amounts for positive or negative deviations. Error limits are mainly specified in relation to systematic errors of the measurement values from the correct value or from another specified or agreed value of the measurement value. It is not permitted for error limits to be exceeded by
random errors. There is a need to differentiate between, for example, maximum permissible error on verification and maximum permissible error in service.

### European Pharmacopeia

    Directory of medicines that was given legal status by the signatory states of the European Pharmacopoeia Convention. The European Pharmacopoeia is published, updated, and expanded by the European Directorate for the Quality of Medicines (EDQM). The mission of the European Pharmacopoeia Convention is to harmonize the standards of the various national European Pharmacopeias as well as the quality standards and control processes for medicines.

### Expansion factor

    Factor $k$ that expands the standard uncertainty $u$ into the uncertainty interval $U$:
    $U=k\cdot u$

### Explosion protection

    Measures to avoid hazardous explosive mixtures of gas and air, or dust and air, and to avoid effective ignition sources.
    In Europe, the intended use of equipment and protective systems in hazardous areas is legally regulated for manufacturers by the ATEX 95 Directive and for operators by the ATEX 137 Directive. The manufacturer must fulfill the essential health and safety requirements defined in the ATEX 95 Directive by suitable construction of the equipment or protective system, and demonstrate fulfillment by corresponding tests. The operator is responsible for avoiding explosive atmospheres and for using suitable equipment or protective systems as intended at the place of installation. Such equipment and protective systems may only be used in hazardous areas if they are constructed in such manner that they cannot act as effective ignition sources.

## F
### Fine dispensing

    Gravimetric or volumetric distribution of a constant or discrete material flow. Coarse dispensing is followed by
fine dispensing to ensure that the prescribed distribution is achieved as accurately as possible.

### Firmware

    Program (software) for the dedicated control of an instrument that is stored in permanent memory. Depending on the memory technology, the firmware may be capable of being updated.

### Fluid

    Substance possessing the physical property of being able to flow. Gases and liquids are fluids.

### Force

    Term first used by Archimedes for the physical quantity that is the cause of all motion or change in shape. There are many sources of force including deformation (spring force), gravitation (weight force, buoyancy), electrostatic and dynamic forces, magnetic forces, kinetic forces (acceleration force, centrifugal force), and friction.
    The SI unit of force is the newton.

### Force measuring cell

    Measurement transducer that converts the input quantity force into, for instance, an electrical output quantity.

## G
### GAMP

    Abbreviation for Good Automated Manufacturing Practice.

### GLP

    Abbreviation for Good Laboratory Practice ([2004/9/EC, 2004/10/EC]).

### GMP

    Abbreviation for Good Manufacturing Practice ([2003/94/EC]).

### Good Automated Manufacturing Practice

    Good Automated Manufacturing Practice (GAMP) is a technical sub-committee, known as a COP (Community Of Practice) of the International Society for Pharmaceutical Engineering (ISPE). The goal of the community is to assist companies in healthcare industries, including pharmaceutical, biotechnology, and medical devices, to achieve validated and compliant automated systems.
    GAMP publishes a series of Good Practice Guides for its members on several topics involved in drug manufacturing. GAMP was founded in 1991 in the United Kingdom to deal with the evolving FDA expectations for Good Manufacturing Practice (GMP) compliance of manufacturing and related systems.

### Good Laboratory Practice

    Good Laboratory Practice (GLP) is a quality assurance system that is concerned with the organizational process and the conditions under which non-clinical health and environmental safety studies are planned, performed, and monitored. GLP is also concerned with recording, archiving, and reporting of the tests.
    The principles of Good Laboratory Practice are applied to the non-clinical safety studies of test items that are included in pharmaceutical products, pesticides, cosmetics, and veterinary drugs, as well as food additives, animal feed additives, and industrial chemicals. The purpose of testing these test items is to obtain data about their properties and/or safety for human health and/or the environment. The tests are initiated by the state authorities responsible for the registration or approval of products in the above-mentioned categories. The OECD GLP Principles of 1997 were adopted as European law and formalized in European Directive [2004/10/EC]. Their verification is regulated in European Directive [2004/9/EC]. Both directives are implemented as national law in the EU.

### Good Manufacturing Practice

    Good Manufacturing Practice (GMP) is a quality assurance system that ensures that products are consistently produced and controlled to the quality standards appropriate to their intended use and as required by the marketing authorization. The prime focus is to avoid cross-contamination (in particular of unexpected contaminants) and mix-ups caused by, for example, false labeling.
    GMP rules exist for various product groups as medicinal products, medical devices, food, or blood. For medicinal products, the rules are formalized in European Directive [2003/94/EC].

### Gravimetry

    1. Method of quantitative analysis in which the mass, or a property that depends upon the mass, is determined by measuring the mass; gravimetric determination.
    2. Theory of the Earth’s gravitational field and methods of determining gravity.

### Gross value

    Indication of the weight value of a load placed on a weighing instrument, with no tare device or preset tare device in operation.

### Gross weight

    Total weight on the platform of a weighing instrument, i.e. the weight of the weighed object (net weight or sample) plus the weight of its container or packaging.

### GxP

    Non official common collective abbreviation for "GLP" (Good Laboratory Practice).

## H
### Halogen lamp

    Infrared heater in which the radiation is produced with the aid of a halogen lamp.

### Hardware

    1. Generic term for mechanical components such as screws, bolts, nuts, etc.
    2. A term that applies to all of the mechanical and electrical components of a computer system or electronic circuit (e.g. printed circuit boards, transistors, integrated circuits, etc.) as well as to entire instruments.

### Housing

    A fixed cover that protects the sensitive parts of a laboratory instrument and prevents inadmissible tampering with the instrument.

### Hydrometer

    Instrument for determining the density of liquids or the concentration of dissolved substances (e.g. Oechsle hydrometer) that takes the form of a glass tube with a scale that floats in the liquid whose density is to be determined. A hydrometer functions on the principle of buoyancy, i.e. it floats higher or lower depending on the density of the liquid.

### Hydrostatic balance

    Balance for determining the density of a liquid by measuring the buoyancy of a sinker in the liquid, or for determining the density of a solid body in a liquid of known density.

### Hysteresis

    The phenomenon that a measuring instrument indicates two different measurement values for the same measurand, depending on whether the measurand is increasing or decreasing. This results in a split characteristic curve: the lower curve is for the increasing, the upper for the decreasing measurand.
    Hysteresis can be compensated for. If hysteresis is overcompensated, the characteristic curve reverses its course.

## I
### Identification mark

    A marking, usually a manufacturer’s number, that is applied to the main devices of the laboratory instrument consisting of separate units to ensure their unambiguous association.

### IEC

    Abbreviation for International Electrotechnical Commission

### ILAC

    International Laboratory Accreditation Cooperation

### Indication

    Value that is represented on a display and can be read (measurement value).

### Influence of moisture

    Air humidity results in an adsorbed film of moisture on virtually all surfaces. An equilibrium between the adsorption film and the surrounding humidity arises. E.g. moisture differences between the sample and the air in the weighing
chamber can thus lead to mass changes in the weighing sample and hence cause drift in the weighing instrument display. Corrective measures include the use of clean, dry weighing vessels. In addition, instead of cork or cardboard surfaces, which may absorb or release a considerable amount of moisture, non-hygroscopic auxiliary equipment (e.g. triangular support) should be used.

### Influence quantities

    1. Quantity that is not the measurand but that affects the result of the measurement.
    2. Quantity that, in a direct measurement, does not affect the quantity that is actually measured, but affects the relation between the indication and the measurement result.

### Inscriptions

    Specifications and designations used for a more detailed description of a laboratory instrument on its data plate and in its operating instructions. The inscriptions may include the name of the manufacturer and the model, serial number, operating voltage and power supply frequency. There may also be references to type data, approval data, instructions, or possible uses and applications of the instrument, etc.

### Installation Qualification

    Part of Equipment Qualification (EQ). The Installation Qualification (IQ) verifies that the instrument is delivered as specified, that it is correctly installed, and that the environment is suitable for its operation.

### Integration time

    The time required by an (electronic) measuring instrument to form a measurement value. The expression derives from the time during which the partial measurement values output by a measurement converter are added (integrated) to form a measurement value with sufficient resolution or stability.
    In the case of digital filters, the integration time is not normally fixed, but comprises an increasing and decreasing weighting
with which completed partial results are summed to form the momentary measurement value.

### Interface

    Point of contact or connection between two data transmission devices. The term "interface" embraces all of the characteristics that describe its physical, electrical, and logical functions at the point of transfer. The characteristics include
those of the plug, the pin assignments, the voltage and current levels, the data format and coding, as well as the data and commands that are transferred.

### International Electrotechnical Commission

    International organization with permanent headquarters in Geneva. The International Electrotechnical Commission (IEC) develops and publishes standards for electrical, electronic, and related technologies.

### International Laboratory Accreditation Cooperation

    International cooperation of laboratory and inspection accreditation bodies to help remove technical barriers to trade. The aim of the ILAC arrangement is the increased use and acceptance by industry as well as regulators of the results from accredited laboratories and inspection bodies, including results from laboratories in other countries.

### International Organization for Legal Metrology

    International organization with permanent headquarters in Paris. The mission of the International Organization for Legal Metrology (OIML) is the international harmonization of the administrative and technical regulations for measurement methods and measuring instruments in the field of legal metrology. For this purpose, the organization
issues recommendations and documents (OIML Recommendations and Documents) for individual measuring instruments.

### International Organization for Standardization

    International organization that has its headquarters in Geneva. The International Organization for Standardization (ISO) undertakes the international standardization of terminology, measurement methods, tolerances, etc. in the industrial field.

### International Prototype of the Kilogram

    Until 2019, it was the definition and representation of the mass unit. This prototype is kept at the International Bureau of Weights and Measures (BIPM), Pavillon de Breteuil, Sèvres, France. The International Prototype of the Kilogram was created and sanctioned by the CIPM in 1889. It is a cylinder with both height and diameter of approximately 39 mm. It is made of an alloy of 90% platinum and 10% iridium with a density of 21500 kg/m3.
    The kilogram was the last of the base units of the International System of Units to be defined by an artefact, i.e., a manufactured object.

### International System of Units

    International system of units, also called SI (abbreviation of the French name "Système international d’unités"), that embodies the metric system of units and is the most widespread system of physical and chemical units.
    The international System of Units has seven base units:
SI base units :
| Dimension | Name | Unit symbol |
| length | meter | m |
| mass | kilogram | kg |
| time | second | s |
| electric current | ampere | A |
| thermodynamic temperature | kelvin | K |
| quantity of substance | mole | mol |
| luminous intensity | candela | cd |
    Other units are derived by means of simple relationships, e.g.: area (m$^{2}$), volume (m$^{3}$), speed (m/s), density (kg/m$^{3}$) ...
    Various derived units have been given specific names and specific unit symbols, e.g.: frequency (hertz Hz), force (newton N), electrical resistance (ohm $\Omega$) ...

### ISO

    Abbreviation for "International Organization for Standardization".

### ISO 17025

    International standard "General Requirements for the Competence of Testing and Calibration Laboratories" which describes the requirements for calibration and testing laboratories. The requirements cover the areas of personnel, technical infrastructure and organizational structure. This insures that the product or service of the laboratory is competently produced or provided and satisfies the requirements.

## K
### k

    Expansion factor.

### kg

    Unit symbol for the mass unit (kilogram).

### Kilogram

    The kilogram (unit symbol "kg") is the unit of mass in the International System of Units. It is one of the seven base units of this system.

## L
### Laboratory balance

    Designation for balances that are mainly used in laboratories and usually referring to precision balances or analytical balances.

### Legal metrology

    Part of metrology relating to activities which result from statutory requirements and concern measurement, units of
measurement, measuring instruments and methods of measurement and which are performed by competent bodies.
    The scope of legal metrology may be different from country to country. The competent bodies responsible for all or part of these legal metrology activities are usually called legal metrology services.

### Legal metrology requirements

    Regulations that must be fulfilled by a measuring instrument to be used in applications subject to legal metrology.

### Level indicator

    Device that indicates the inclination. A level indicator usually comprises a sealed container (of glass or clear plastic) that is filled with liquid on which a gas bubble floats. Depending on the application, different shapes such as tubular, cross-shaped or circular level indicators are used.

### Level, to

    Adjusting a laboratory instrument to its reference position (usually horizontal) so that its axis of action is parallel to
the vertical. This usually means setting the housing of the instrument horizontal.