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Calibration Terminology

Accreditation (of a laboratory) - Formal recognition by an accreditation body that a calibration or testing laboratory is able to competently perform the calibrations or tests listed in the accreditation scope document. Accreditation includes evaluation of both the quality management system and the competence to perform the measurements listed in the scope.

Accreditation body - An organization that conducts laboratory accreditation evaluations in conformance to ISO Guide 58.

Accreditation certificate - Document issued by an accreditation body to a laboratory that has met the conditions and criteria for accreditation. The certificate, with the documented measurement parameters and their best uncertainties, serves as proof of accredited status for the time period listed. An accreditation certificate without the documented parameters is incomplete.
Accreditation criteria – Set of requirements used by an accrediting body that a laboratory must meet in order to be accredited.

Accuracy (of a measurement) - Accuracy is a qualitative indication of how closely the result of a measurement agrees with the true value of the parameter being measured. (VIM, 3.5) Because the true value is always unknown, accuracy of a measurement is always an estimate. An accuracy statement by itself has no meaning other than as an indicator of quality. It has quantitative value only when accompanied by information about the uncertainty of the measuring system. Contrast with: accuracy (of a measuring instrument)

Accuracy (of a measuring instrument) - Accuracy is a qualitative indication of the ability of a measuring instrument to give responses close to the true value of the parameter being measured. (VIM, 5.18) Accuracy is a design specification and may be verified during calibration. Contrast with: accuracy (of a measurement)

Assessment - Examination typically performed on-site of a testing or calibration laboratory to evaluate its conformance to conditions and criteria for accreditation.

Best measurement capability - For an accredited laboratory, the best measurement capability for a particular quantity is "the smallest uncertainty of measurement a laboratory can achieve within its scope of accreditation when performing more or less routine calibrations of nearly ideal measurement standards intended to define, realize, conserve, or reproduce a unit of that quantity or one or more of its values; or when performing more-or-less routine calibrations of nearly ideal measuring instruments designed for the measurement of that quantity." (EA-4/02) The best measurement capability is based on evaluations of actual measurements using generally accepted methods of evaluating measurement uncertainty.

Bias - Bias is the known systematic error of a measuring instrument. (VIM, 5.25) The value and direction of the bias is determined by calibration and/or gage R&R studies. Adding a correction, which is always the negative of the bias, compensates for the bias. See also: correction, systematic error

Calibration - (1). (See VIM 6.11 and NCSL pages 4-5 for primary and secondary definitions.) Calibration is a term that has many different - but similar - definitions. It is the process of verifying the capability and performance of an item of measuring and test equipment by comparison to traceable measurement standards. Calibration is performed with the item being calibrated in its normal operating configuration - as the normal operator would use it. The calibration process uses traceable external stimuli, measurement standards, or artifacts as needed to verify the performance. Calibration provides assurance that the instrument is capable of making measurements to its performance specification when it is correctly used. The result of a calibration is a determination of the performance quality of the instrument with respect to the desired specifications. This may be in the form of a pass/fail decision, determining or assigning one or more values, or the determination of one or more corrections. The calibration process consists of comparing an IM&TE unit with specified tolerances, but of unverified accuracy, to a measurement system or device of specified capability and known uncertainty in order to detect, report, or minimize by adjustment any deviations from the tolerance limits or any other variation in the accuracy of the instrument being compared. Calibration is performed according to a specified documented calibration procedure, under a set of specified and controlled measurement conditions, and with a specified and controlled measurement system.

Notes:

• A requirement for calibration does not imply that the item being calibrated can or should be adjusted.

• The calibration process may include, if necessary, calculation of correction factors or adjustment of the instrument being compared to reduce the magnitude of the inaccuracy.

• In some cases, minor repair such as replacement of batteries, fuses, or lamps, or minor adjustment such as zero and span, may be included as part of the calibration.

• Calibration does not include any maintenance or repair actions except as just noted. See also: performance test, calibration procedure Contrast with: calibration (2) and repair

Calibration - 2 A) Many manufacturers incorrectly use the term calibration to name the process of alignment or adjustment of an item that is either newly manufactured or is known to be out of tolerance, or is otherwise in an indeterminate state. Many calibration procedures in manufacturers' manuals are actually factory alignment procedures that only need to be performed if a UUC is in an indeterminate state because it is being manufactured, is known to be out of tolerance, or after it is repaired. When used this way, calibration means the same as alignment or adjustment, which are repair activities and excluded from the metrological definition of calibration.
(B) In many cases, IM&TE instruction manuals may use calibration to describe tasks normally performed by the operator of a measurement system. Examples include performing a self-test as part of normal operation or performing a self-calibration (normalizing) a measurement system before use. When calibration is used to refer to tasks like this, the intent is that they are part of the normal work done by a trained user of the system. These and similar tasks are excluded from the metrological definition of calibration. Contrast with: calibration (1) See also: normalization, self-calibration, standardization

Calibration activity or provider - A laboratory or facility - including personnel - that perform calibrations in an established location or at customer location(s). It may be external or internal, including subsidiary operations of a larger entity. It may be called a calibration laboratory, shop, or department; a metrology laboratory or department; or an industry-specific name; or any combination or variation of these.

Calibration certificate - (1) A calibration certificate is generally a document that states that a specific item was calibrated by an organization. The certificate identifies the item calibrated, the organization presenting the certificate, and the effective date. A calibration certificate should provide other information to allow the user to judge the adequacy and quality of the calibration. (2) In a laboratory database program, a certificate often refers to the permanent record of the final result of a calibration. A laboratory database certificate is a record that cannot be changed; if it is amended later a new certificate is created. See also: calibration report

Calibration procedure - A calibration procedure is a controlled document that provides a validated method for evaluating and verifying the essential performance characteristics, specifications, or tolerances for a model of measuring or testing equipment. A calibration procedure documents one method of verifying the actual performance of the item being calibrated against its performance specifications. It provides a list of recommended calibration standards to use for the calibration; a means to record quantitative performance data both before and after adjustments; and information sufficient to determine if the unit being calibrated is operating within the necessary performance specifications. A calibration procedure always starts with the assumption that the unit under test is in good working order and only needs to have its performance verified. Note: A calibration procedure does not include any maintenance or repair actions.

Calibration program - A calibration program is a process of the quality management system that includes management of the use and control of calibrated inspection, and test and measuring equipment (IM&TE), and the process of calibrating IM&TE used to determine conformance to requirements or used in supporting activities. A calibration program may also be called a measurement management system (ISO 10012:2003).

Calibration report - A calibration report is a document that provides details of the calibration of an item. In addition to the basic items of a calibration certificate, a calibration report includes details of the methods and standards used, the parameters checked, and the actual measurement results and uncertainty. See also: calibration certificate

Calibration seal - A calibration seal is a device, placard, or label that, when removed or tampered with, and by virtue of its design and material, clearly indicates tampering. The purpose of a calibration seal is to ensure the integrity of the calibration. A calibration seal is usually imprinted with a legend similar to "Calibration Void if Broken or Removed" or "Calibration Seal - Do Not Break or Remove." A calibration seal provides a means of deterring the user from tampering with any adjustment point that can affect the calibration of an instrument and detecting an attempt to access controls that can affect the calibration of an instrument. Note: A calibration seal may also be referred to as a tamper seal.

Calibration standard - (See VIM, 6.1 through 6.9, and 6.13, 6.14; and NCSL pages 36-38.) A calibration standard is an IM&TE item, artifact, standard reference material, or measurement transfer standard that is designated as being used only to perform calibrations of other IM&TE items. As calibration standards are used to calibrate other IM&TE items, they are more closely controlled and characterized than the workload items they are used for. Calibration standards generally have lower uncertainty and better resolution than general-purpose items. Designation as a calibration standard is based on the use of the specific instrument, however, not on any other consideration. For example, in a group of identical instruments, one might be designated as a calibration standard while the others are all general purpose IM&TE items. Calibration standards are often called measurement standards. See also: standard (measurement) Combined standard uncertainty - The standard uncertainty of the result of a measurement, when that result is obtained from the values of a number of other quantities. It is equal to the positive square root of a sum of terms. The terms are the variances or covariances of these other quantities, weighted according to how the measurement result varies with changes in those quantities. (GUM, 2.3.4) See also: expanded uncertainty

Competence - For a laboratory, the demonstrated ability to perform the tests or calibrations within the accreditation scope and to meet other criteria established by the accreditation body. For a person, the demonstrated ability to apply knowledge and skills. Note: The word qualification is sometimes used in the personal sense, since it is a synonym and has more accepted usage in the United States.

Confidence interval - A range of values that is expected to contain the true value of the parameter being evaluated with a specified level of confidence. The confidence interval is calculated from sample statistics. Confidence intervals can be calculated for points, lines, slopes, standard deviations, and so on. For an infinite (or very large compared to the sample) population, the confidence interval is:

where

CI is the confidence interval,
n is the number of items in the sample,
p is the proportion of items of a given type in the population,
s is the sample standard deviation,
x is the sample mean, and
t is the Student’s T value for α⁄2 and (n – 1) (α is the level of significance).

Correction (of error) - A correction is the value that is added to the raw result of a measurement to compensate for known or estimated systematic error or bias. (VIM, 3.15) Any residual amount is treated as random error. The correction value is equal to the negative of the bias. An example is the value calculated to compensate for the calibration difference of a reference thermometer or for the calibrated offset voltage of a thermocouple reference junction. See also: bias, error, random error, systematic error Corrective action - Corrective action is something done to correct a nonconformance when it arises, including actions taken to prevent reoccurrence of the nonconformance. Compare with: preventive action

Coverage factor - A numerical factor used as a multiplier of the combined standard uncertainty in order to obtain an expanded uncertainty. (GUM, 2.3.6) The coverage factor is identified by the symbol k. It is usually given the value 2, which approximately corresponds to a probability of 95 percent for degrees of freedom > 10'.

Deficiency - Nonfulfillment of conditions and/or criteria for accreditation, sometimes referred to as a nonconformance.

Departure value - A term used by a few calibration laboratories to refer to bias, error or systematic error. The exact meaning can usually be determined from examination of the calibration certificate.
Equivalence - (A) Acceptance of the competence of other national metrology institutes (NMI), accreditation bodies, and/or accredited organizations in other countries as being essentially equal to the NMI, accreditation body, and/or accredited organizations within the host country.
(B) A formal, documented determination that a specific instrument or type of instrument is suitable for use in place of the one originally listed, for a particular application.

Error (of measurement) - (See VIM, 3.10, 3.12-3.14; and NCSL pages 11-13.) In metrology, error (or measurement error) is an estimate of the difference between the measured value and the probable true value of the object of the measurement. The error can never be known exactly; it is always an estimate. Error may be systematic and/or random. Systematic error (also known as bias) may be corrected. See also: bias, correction (of error), random error, systematic error

Gage R&R - Gage repeatability and reproducibility study, which (typically) employs numerous instruments, personnel, and measurements over a period of time to capture quantitative observations. The data captured are analyzed statistically to obtain best measurement capability, which is expressed as an uncertainty with a coverage factor of k = 2 to approximate 95 percent. The number of instruments, personnel, measurements, and length of time are established to be statistically valid consistent with the size and level of activity of the organization.

GUM - An acronym commonly used to identify the ISO Guide to the Expression of Uncertainty in Measurement. In the United States, the equivalent document is ANSI/NCSL Z540-2-1997, U. S. Guide to the Expression of Uncertainty in Measurement.

IM&TE - The acronym IM&TE refers to inspection, measuring, and test equipment. This term includes all items that fall under a calibration or measurement management program. IM&TE items are typically used in applications where the measurement results are used to determine conformance to technical or quality requirements before, during, or after a process. Some organizations do not include instruments used solely to check for the presence or absence of a condition (such as voltage, pressure, and so on) where a tolerance is not specified and the indication is not critical to safety. Note: Organizations may refer to IM&TE items as MTE (measuring and testing equipment), TMDE (test, measuring, and diagnostic equipment), GPETE (general purpose electronic test equipment), PME (precision measuring equipment), PMET (precision measuring equipment and tooling), or SPETE (special purpose electronic test equipment).

Interlaboratory comparison - Organization, performance, and evaluation of tests or calibrations on the same or similar items or materials by two or more laboratories in accordance with predetermined conditions.

Internal audit - A systematic and documented process for obtaining audit evidence and evaluating it objectively to verify that a laboratory's operations comply with the requirements of its quality system. An internal audit is done by or on behalf of the laboratory itself, so it is a first-party audit.

International Organization for Standardization (ISO) - An international nongovernmental organization chartered by the United Nations in 1947, with headquarters in Geneva, Switzerland. The mission of ISO is "to promote the development of standardization and related activities in the world with a view to facilitating the international exchange of goods and services, and to developing cooperation in the spheres of intellectual, scientific, technological and economic activity." The scope of ISO's work covers all fields of business, industry and commerce except electrical and electronic engineering. The members of ISO are the designated national standards bodies of each country. (The United States is represented by ANSI.) See also: ISO

International System of Units (SI) - A defined and coherent system of units adopted and used by international treaties. (The acronym SI is from the French Systéme International.) SI is international system of measurement for all physical quantities. (Mass, length, amount of substance, time, electric current, thermodynamic temperature, and luminous intensity.) SI units are defined and maintained by the International Bureau of Weights and Measures (BIPM) in Paris, France. The SI system is popularly known as the metric system.

ISO - Iso is a Greek word root meaning equal. The International Organization for Standardization chose the word as the short form of the name, so it will be a constant in all languages. In this context, ISO is not an acronym. (If the acronym was based on the full name were used, it would be different in each language.) The name also symbolizes the mission of the organization - to equalize standards worldwide.

Level of confidence - Defines an interval about the measurement result that encompasses a large fraction p of the probability distribution characterized by that result and its combined standard uncertainty, and p is the coverage probability or level of confidence of the interval. Effectively, the coverage level expressed as a percent.

Management review - The planned, formal, periodic, and scheduled examination of the status and adequacy of the quality management system in relation to its quality policy and objectives by the organization's top management.

Measurement - A set of operations performed for the purpose of determining the value of a quantity. (VIM, 2.1)

Measurement system - A measurement system is the set of equipment, conditions, people, methods, and other quantifiable factors that combine to determine the success of a measurement process. The measurement system includes at least the test and measuring instruments and devices, associated materials and accessories, the personnel, the procedures used, and the physical environment.

Metrology - Metrology is the science and practice of measurement (VIM, 2.2).

Mobile operations - Operations that are independent of an established calibration laboratory facility. Mobile operations may include work from an office space, home, vehicle, or the use of a virtual office.

Natural (physical) constant - A natural constant is a fundamental value that is accepted by the scientific community as valid. Natural constants are used in the basic theoretical descriptions of the universe. Examples of natural physical constants important in metrology are the speed of light in a vacuum (c), the triple point of water (273.16 K), the quantum charge ratio (h/e), the gravitational constant (G), the ratio of a circle's circumference to its diameter (p), and the base of natural logarithms (e).

NCSL international - Formerly known as the National Conference of Standards Laboratories (NCSL). NCSL was formed in 1961 to "promote cooperative efforts for solving the common problems faced by measurement laboratories. NCSL has member organizations from academic, scientific, industrial, commercial and government facilities around the world. NCSL is a nonprofit organization, whose membership is open to any organization with an interest in the science of measurement and its application in research, development, education, or commerce. NCSL promotes technical and managerial excellence in the field of metrology, measurement standards, instrument calibration, and test and measurement."

Normalization, Normalize - See: self-calibration

Offset - Offset is the difference between a nominal value (for an artifact) or a target value (for a process) and the actual measured value. For example, if the thermocouple alloy leads of a reference junction probe are formed into a measurement junction and placed in an ice point cell, and the reference junction itself is also in the ice point, then the theoretical thermoelectric emf measured at the copper wires should be zero. Any value other than zero is an offset created by inhomogeneity of the thermocouple wires combined with other uncertainties. Compare with: bias, error

On-site operations - Operations that are based in or directly supported by an established calibration laboratory facility, but actually perform the calibration actions at customer locations. This includes climate-controlled mobile laboratories.

Performance Test - A performance test (or performance verification) is the activity of verifying the performance of an item of measuring and test equipment to provide assurance that the instrument is capable of making correct measurements when it is properly used. A performance test is done with the item in its normal operating configuration. A performance test is the same as a calibration (1). See also: calibration (1)

Policy - A policy defines and sets out the basic objectives, goals, vision, or general management position on a specific topic. A policy describes what management intends to have done regarding a given portion of business activity. Policy statements relevant to the quality management system are generally stated in the quality manual. Policies can also be in the organization's policy/procedure manual. See also: procedure

Precision - Precision is a property of a measuring system or instrument. Precision is a measure of the repeatability of a measuring system - how much agreement there is within a group of repeated measurements of the same quantity under the same conditions. (NCSL, page 26) Precision is not the same as accuracy. (VIM, 3.5)

Preventive action - Preventive action is something done to prevent the possible future occurrence of a nonconformance, even though such an event has not yet happened. Preventive action helps improve the system. Contrast with: corrective action

Procedure - A procedure describes a specific process for implementing all or a portion of a policy. There may be more than one procedure for a given policy. A procedure has more detail than a policy but less detail than a work instruction. The level of detail needed should correlate with the level of education and training of the people with the usual qualifications to do the work and the amount of judgment normally allowed to them by management. Some policies may be implemented by fairly detailed procedures, while others may only have a few general guidelines. Calibration: see calibration procedure. See also: policy

Proficiency testing - Determination of laboratory testing performance by means of interlaboratory comparisons.

Quality manual - The quality manual is the document that describes the quality management policy of an organization with respect to a specified conformance standard. The quality manual briefly defines the general policies as they apply to the specified conformance standard and affirms the commitment of the organization's top management to the policy. In addition to its regular use by the organization, auditors use the quality manual when they audit the quality management system. The quality manual is generally provided to customers on request. Therefore, it does not usually contain any detailed policies and never contains any procedures, work instructions, or proprietary information.

Random error - Random error is the result of a single measurement of a value, minus the mean of a large number of measurements of the same value. (VIM, 3.13) Random error causes scatter in the results of a sequence of readings and, therefore, is a measure of dispersion. Random error is usually evaluated by Type A methods, but Type B methods are also used in some situations. Note: Contrary to popular belief, the GUM specifically does not replace random error with either Type A or Type B methods of evaluation. See also: error Compare with: systematic error

Repair - Repair is the process of returning an unserviceable or nonconforming item to serviceable condition. The instrument is opened, or has covers removed, or is removed from its case and may be disassembled to some degree. Repair includes adjustment or alignment of the item as well as component-level repair. (Some minor adjustment such as zero and span may be included as part of the calibration.) The need for repair may be indicated by the results of a calibration. For calibratable items, repair is always followed by calibration of the item. Passing the calibration test indicates success of the repair. Contrast with: calibration (1), repair (minor)

Repair (minor) - Minor repair is the process of quickly and economically returning an unserviceable item to serviceable condition by doing simple work using parts that are in stock in the calibration lab. Examples include replacement of batteries, fuses, or lamps; or minor cleaning of switch contacts; or repairing a broken wire; or replacing one or two in-stock components. The need for repair may be indicated by the results of a calibration. For calibratable items, minor repair is always followed by calibration of the item. Passing the calibration test indicates success of the repair. Minor repairs are defined as repairs that take no longer than a short time as defined by laboratory management, and where no parts have to be ordered from external suppliers, and where substantial disassembly of the instrument is not required. Contrast with: calibration (1), repair

Reported value - One or more numerical results of a calibration process, with the associated measurement uncertainty, as recorded on a calibration report or certificate. The specific type and format vary according to the type of measurement being made. In general, most reported values will be in one of these formats:

• Measurement result and uncertainty. The reported value is usually the mean of a number of repeat measurements. The uncertainty is usually expanded uncertainty as defined in the GUM.

• Deviation from the nominal (or reference) value and uncertainty. The reported value is the difference between the nominal value and the mean of a number of repeat measurements. The uncertainty of the deviation is usually expanded uncertainty as defined in the GUM.

• Estimated systematic error and uncertainty. The value may be reported this way when it is known that the instrument is part of a measuring system and the systematic error will be used to calculate a correction that will apply to the measurement system results.

Round robin - See: Interlaboratory Comparison

Scope of accreditation - For an accredited calibration or testing laboratory, the scope is a documented list of calibration or testing fields, parameters, specific measurements, or calibrations and their best measurement, uncertainty. The scope document is an attachment to the certificate of accreditation and the certificate is incomplete without it. Only the calibration or testing areas that the laboratory is accredited for are listed in the scope document, and only the listed areas may be offered as accredited calibrations or tests. The accreditation body usually defines the format and other details.

Self-calibration - Self-calibration is a process performed by a user for the purpose of making an IM&TE instrument or system ready for use. The process may be required at intervals such as every power-on sequence; or once per shift, day, or week of continuous operation; or if the ambient temperature changes by a specified amount. Once initiated, the process may be performed totally by the instrument or may require user intervention and/or use of external calibrated artifacts. The usual purpose is accuracy enhancement by characterization of errors inherent in the measurement system before the item to be measured is connected. Self-calibration is not equivalent to periodic calibration (performance verification) because it is not performed using a calibration procedure and does not meet the metrological requirements for calibration. Also, if an instrument requires self-calibration before use, then that will also be accomplished at the start of a calibration procedure. Self-calibration may also be called normalization or standardization. Compare with: calibration (2.B) Contrast with: calibration (1)

Specification - In metrology, a specification is a documented statement of the expected performance capabilities of a large group of substantially identical measuring instruments, given in terms of the relevant parameters and including the accuracy or uncertainty. Customers use specifications to determine the suitability of a product for their own applications. A product that performs outside the specification limits when tested (calibrated) is rejected for later adjustment, repair, or scrapping.

Standard (document) - A standard (industry, national, government, or international standard; a norme) is a document that describes the processes and methods that must be performed in order to achieve a specific technical or management objective, or the methods for evaluation of any of these. An example is ANSI/NCSL Z540-1-1994, a national standard that describes the requirements for the quality management system of a calibration organization and the requirements for calibration and management of the measurement standards used by the organization.

Standard (measurement) - A standard (measurement standard, laboratory standard, calibration standard, reference standard; an étalon) is a system, instrument, artifact, device, or material that is used as a defined basis for making quantitative measurements. The value and uncertainty of the standard define a limit to the measurements that can be made: a laboratory can never have better precision or accuracy than its standards. Measurement standards are generally used in calibration laboratories. Items with similar uses in a production shop are generally regarded as working-level instruments by the calibration program.
Primary standard. Accepted as having the highest metrological qualities and whose value is accepted without reference to other standards of the same quantity. Examples: triple point of water cell and caesium beam frequency standard.
Transfer standard. A device used to transfer the value of a measurement quantity (including the associated uncertainty) from a higher level to a lower level standard.
Secondary standard. The highest accuracy level standards in a particular laboratory generally used only to calibrate working standards. Also called a reference standard.
Working standard. A standard that is used for routine calibration of IM&TE. The highest level standards, found in national and international metrology laboratories, are the realizations or representations of SI units. See also: calibration standard

Standard operating procedure (SOP) - A term used by some organizations to identify policies, procedures, or work instructions.

Standard reference material - A standard reference material (SRM) as defined by NIST "is a material or artifact that has had one or more of its property values certified by a technically valid procedure, and is accompanied by, or traceable to, a certificate or other documentation which is issued by NIST. Standard reference materials are.manufactured according to strict specifications and certified by NIST for one or more quantities of interest. SRMs represent one of the primary vehicles for disseminating measurement technology to industry."

Standard uncertainty - The uncertainty of the result of a measurement, expressed as a standard deviation. (GUM, 2.3.1)

Standardization - See: self-calibration.

Systematic error - A systematic error is the mean of a large number of measurements of the same value minus the (probable) true value of the measured parameter. (VIM, 3.14) Systematic error causes the average of the readings to be offset from the true value. Systematic error is a measure of magnitude and may be corrected. Systematic error is also called bias when it applies to a measuring instrument. Systematic error may be evaluated by Type A or Type B methods, according to the type of data available. Note: Contrary to popular belief, the GUM specifically does not replace systematic error with either Type A or Type B methods of evaluation. (3.2.3, note) See also: bias, error, correction (of error) Compare with: random error

Test accuracy ratio - (1) In a calibration procedure, the test accuracy ratio (TAR) is the ratio of the accuracy tolerance of the unit under calibration to the accuracy tolerance of the calibration standard used. (NCSL, page 2)

TAR = UUT_tolerance
STD_tolerance
The TAR must be calculated using identical parameters and units for the UUC and the calibration standard. If the accuracy tolerances are expressed as decibels, percentage, or another ratio, they must be converted to absolute values of the basic measurement units. (2) In the normal use of IM&TE items, the TAR is the ratio of the tolerance of the parameter being measured to the accuracy tolerance of the IM&TE. Note: TAR may also be referred to as the accuracy ratio or (incorrectly) the uncertainty ratio.

Test uncertainty ratio - In a calibration procedure, the test uncertainty ratio (TUR) is the ratio of the accuracy tolerance of the unit under calibration to the uncertainty of the calibration standard used. (NCSL, page 2)

TUR = UUT_tolerance
STD_uncert
The TUR must be calculated using identical parameters and units for the UUC and the calibration standard. If the accuracy tolerances are expressed as decibels, percentage, or another ratio, they must be converted to absolute values of the basic measurement units. Note: The uncertainty of a measurement standard is not necessarily the same as its accuracy specification.

Tolerance - A tolerance is a design feature that defines limits within which a quality characteristic is supposed to be on individual parts; it represents the maximum allowable deviation from a specified value. Tolerances are applied during design and manufacturing. A tolerance is a property of the item being measured. Compare with: specification, uncertainty

Traceable, traceability - Traceability is a property of the result of a measurement, providing the ability to relate the measurement result to stated references, through an unbroken chain of comparisons each having stated uncertainties. (VIM, 6.10) Traceability is a demonstrated or implied property of the result of a measurement to be consistent with an accepted standard within specified limits of uncertainty. (NCSL, pages 42-43) The stated references are normally the base or supplemental SI units as maintained by a national metrology institute; fundamental or physical natural constants that are reproducible and have defined values; ratio type comparisons; certified standard reference materials; or industry or other accepted consensus reference standards. Traceability provides the ability to demonstrate the accuracy of a measurement result in terms of the stated reference. Measurement assurance methods applied to a calibration system include demonstration of traceability. A calibration system operating under a program controls system only implies traceability. Evidence of traceability includes the calibration report (with values and uncertainty) of calibration standards, but the report alone is not sufficient. The laboratory must also apply and use the data. A calibration laboratory, a measurement system, a calibrated IM&TE, a calibration report, or any other thing is not and be traceable to a national standard. Only the result of a specific measurement can be said to be traceable, provided all of the conditions just listed are met. Reference to a NIST test number is specifically not evidence of traceability. That number is merely a catalog number of the specific service provided by NIST to a customer so it can be identified on a purchase order.

Transfer measurement - A transfer measurement is a type of method that enables making a measurement to a higher level of resolution than normally possible with the available equipment. Common transfer methods are differential measurements and ratio measurements.

Transfer standard - A transfer standard is a measurement standard used as an intermediate device when comparing two other standards. (VIM, 6.8) Typical applications of transfer standards are to transfer a measurement parameter from one organization to another, from a primary standard to a secondary standard, or from a secondary standard to a working standard in order to create or maintain measurement traceability. Examples of typical transfer standards are DC volt sources (standard cells or zener sources), and single-value standard resistors, capacitors, or inductors.

Type A evaluation (of uncertainty) - Type A evaluation of measurement uncertainty is the statistical analysis of actual measurement results to produce uncertainty values. Both random and systematic error may be evaluated by Type A methods. (GUM, 3.3.3 through 3.3.5) Uncertainty can only be evaluated by Type A methods if the laboratory actually collects the data.

Type B evaluation (of uncertainty) - Type B evaluation of measurement uncertainty includes any method except statistical analysis of actual measurement results. Both random and systematic error may be evaluated by Type B methods. (GUM, 3.3.3 through 3.3.5) Data for evaluation by Type B methods may come from any source believed to be valid.

Uncertainty - Uncertainty is a property of a measurement result that defines the range of probable values of the measurand. Total uncertainty may consist of components that are evaluated by the statistical probability distribution of experimental data or from assumed probability distributions based on other data. Uncertainty is an estimate of dispersion; effects that contribute to the dispersion may be random or systematic. (GUM, 2.2.3) Uncertainty is an estimate of the range of values that the true value of the measurement is within, with a specified level of confidence. After an item that has a specified tolerance has been calibrated using an instrument with a known accuracy, the result is a value with a calculated uncertainty. See also: Type A evaluation, Type B evaluation

Uncertainty budget - The systematic description of known uncertainties relevant to specific measurements or types of measurements, categorized by type of measurement, range of measurement, and/or other applicable measurement criteria.

UUC, UUT - The unit under calibration or the unit under test - the instrument being calibrated. These are standard generic labels for the IM&TE item that is being calibrated, which are used in the text of the calibration procedure for convenience. Also may be called device under test (DUT) or equipment under test (EUT).

Validation - Substantiation by examination and provision of objective evidence that verified processes, methods, and/or procedures are fit for their intended use.

Verification - Confirmation by examination and provision of objective evidence that specified requirements have been fulfilled.

VIM - An acronym commonly used to identify the ISO International Vocabulary of Basic and General Terms in Metrology. (The acronym comes from the French title.)

Work Instruction - In a quality management system, a work instruction defines the detailed steps necessary to carry out a procedure. Work instructions are used only where they are needed to ensure the quality of the product or service. The level of education and training of the people with the usual qualifications to do the work must be considered when writing a work instruction. In a metrology laboratory, a calibration procedure is a type of work instruction.