IAS GUIDE FOR REPRESENTING SCOPES OF ACCREDITATION FOR
CALIBRATION LABORATORIES
1. INTRODUCTION AND SCOPE
This document provides IAS guidelines for the representation of a calibration laboratory’s scopeof accreditation. The scope of accreditation document represents an accreditation body’s official
declaration of a laboratory’s calibration and measurement capabilities (CMC) and attests to thefact that the laboratory has the technical competence to perform the activities listed on thisdocument. It also serves as a means to provide the customer of an accredited calibrationlaboratory with a clear description of a laboratory’s activities covered by their ISO/IEC 17025
accreditation.
The purpose of this guide is to outline the IAS requirements for calibration scopes ofaccreditation, and to establish guidelines that minimize sources of variability in order to ensurethat all IAS scopes of accreditation for calibration laboratories are similar in appearance anddisplay similar levels of detail.
2. DEFINITIONSBIPM: International Bureau of Weights and Measures. The BIPM is the international organization established by the Metre Convention, through whichMember States act together on matters related to measurement science andmeasurement standards
 the home of the International System of Units (SI) and the international reference timescale (UTC).”(https://www.bipm.org/)CALIBRATION AND MEASUREMENT CAPABILITY (CMC): A CMC is a calibration andmeasurement capability available to customers under normal conditions: (a) as published in theBIPM key comparison database (KCDB) of the CIPM MRA; or (b) as described in the laboratory’s
scope of accreditation granted by a signatory to the ILAC Arrangement. (ILAC-P14:09/2020)
CGPM: General Conference on Weights and Measures. The CGPM is the primaryintergovernmental treaty organization responsible for the SI, representing nearly 50 countries.
It has the responsibility of ensuring that the SI is widely disseminated and modifying it as

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necessary so that it reflects the latest advances(https://physics.nist.gov/cuu/Units/acronyms.html)

inscienceandtechnology.

CIPM: International Committee for Weights and Measures. The CIPM comes under the authorityof the CGPM. It suggests modifications to the SI to the CGPM for formal adoption. The CIPM
may also on its own authority pass clarifying resolutions and recommendations regarding the SI.
(https://physics.nist.gov/cuu/Units/acronyms.html)
ILAC: The International Laboratory Accreditation Cooperation.
(http://www.ilac.org)
INTERNATIONAL SYSTEM OF UNITS (SI): System of units, based on the International Systemof Quantities, their names and symbols, including a series of prefixes and their names andsymbols, together with rules for their use, adopted by the General Conference of Weights andMeasures (CGPM). (JCGM 200:2012).
NIST: National Institute of Standards and Technology, the NMI for the U.S.
(http://www.nist.gov)
NMI: National Metrology Institute or National Measurement Institute
3. GUIDELINES
3.1. All scopes of accreditation for calibration laboratories must comply with the requirementsof ILAC-P14, ILAC Policy for Uncertainty in Calibration. While this guidance document
does not repeat all the ILAC requirements stated in ILAC-P14, all ILAC policies must be
followed when formulating scopes of accreditation. In addition, this document takes into
account the guidance provided in ILAC-G18, Guideline for describing Scopes ofAccreditation,
3.2. While the representation of physical quantities in SI units is preferred, IAS recognizes
that it is oftentimes necessary for a laboratory to describe its CMC in the units used when
performing the calibrations and desired by its customers, in order to provide its customers
with a clear and unambiguous description of its capabilities. IAS therefore allows
representation of CMC in non-SI units, as needed. Conversion to SI units, whereapplicable, can be achieved by applying conversion factors as outlined in NIST Special
Publication 811.
3.3. Minimum requirements for scope
3.3.1. Calibration Discipline
The scope of accreditation for calibration laboratories is grouped into general calibration
disciplines: Dimensional, Mechanical, Thermal, Electrical (DC/Low Frequency), Time andFrequency, RF/Microwave and Electromagnetics, Optical Radiation, Chemical/Gas.
3.3.2. Calibration and Measurement Capability (CMC)

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The contents of the four columns in the scope of accreditation serves to define theaccredited laboratory’s CMC.
3.3.2.1.

Measured Quantity or Device Type Calibrated

This column is used to describe either the type of calibration item, e.g. caliper,
micrometer, timer/stopwatch, etc., or the physical quantity to be measured orgenerated in a more generic form, e.g. Voltage-Measure, Current-Generate orCurrent-Source. The term “Generate” or “Source” may be used to indicate thegeneration of physical parameters, when the calibration is performed by generatingor sourcing a known physical quantity. While the two terms are considered
equivalent, the laboratory should be consistent in using one or the other in their
particular scope. Similarly, the term “Measure” is used to indicate that thelaboratory has the capability of measuring a physical quantity generated by thedevice under calibration. These generic parameters are always accompanied by afootnote which generically describes the type of device that can be calibrated withthis capability.
3.3.2.2.

Range

This indicates over which range the stated expanded uncertainty can be achieved.
The beginning and end of the range should be properly defined. Open ranges
must be avoided, since they lead to ambiguity (e.g. range statements such as“above 500 ºC” are not allowed).
3.3.2.3.

Uncertainty

3.3.2.3.1.
The uncertainty stated on the scope of accreditation must be
expressed as the expanded uncertainty with a coverage probability of
approximately 95%. It represents the smallest measurement uncertainty
that a laboratory can achieve within its scope of accreditation when
performing more or less routine calibrations of a best existing device.
3.3.2.3.2.
Note that uncertainties should be stated in the same unit as thecalibration quantity, or relative to that quantity, e.g. percent. Whenuncertainty is expressed as a relative quantity, it usually is relative to theinstrument reading or instrument output quantity. IAS has chosen to
include the following footnote in its scope template: “When uncertainty isstated in relative terms (such as percent, a multiplier expressed as adecimal fraction or in scientific notation), it is in relation to instrument
reading or instrument output, as appropriate, unless otherwise indicated.”This allows us to avoid repeated statements of “% of reading” or “% ofoutput.” However, if a laboratory wishes to express the uncertainty as %of range or % of full scale, it will be specifically indicated on the scope.
3.3.2.3.3.
When stating CMC uncertainties applicable to a range ofmeasurements, care must be taken to avoid ambiguity. The reader of thescope must be able to deduce the measurement uncertainty the laboratory
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is capable of achieving at any given point in the range. To this end, thelaboratory can choose to express its CMC uncertainty in one of thefollowing ways:
3.3.2.3.3.1.
A single value valid throughout the range. This stateduncertainty must be achievable throughout the range, hence it may benecessary to overstate the uncertainty for some parts of the range.
Sub-ranges can be created to avoid severe overstatement ofuncertainties.
3.3.2.3.3.2.
Uncertainties expressed as a range, e.g. 1 nm to 10 nm. Thisis only acceptable if linear interpolation between uncertainty range
endpoints accurately reflects the uncertainties that can be achieved
for any given point in the measurement range.
3.3.2.3.3.3.
An explicit function of a measurand and/or parameter, e.g.
0.045 % of reading + 15 mV.
3.3.2.3.3.4.
Matrix or graphical representation may be possible and will be
discussed with the laboratory on an individual basis.
3.3.2.4.

Calibration Method or Procedure, Standard Equipment (Optional)

This section of the scope is used to provide information about the calibration
method or calibration procedure, and the equipment used to achieve the CMC (thelatter is optional). The calibration or measurement method must be stated, but a
specific internal calibration procedure number or title is not required, as long as thegeneral methodology of the calibration is stated. Listing the standard equipment
is optional unless necessary to convey the general methodology. Note that if apublished method is cited, it is assumed that the latest published version of themethod is applied, unless there is a valid reason not to do so. In this case, thepublication year of the outdated method must be identified. If the laboratory usesa modified version of the method, this must also be indicated.
3.4. Additional guidelines
3.4.1. Unit symbols
3.4.1.1. Symbols for SI and non-SI units as indicated in NIST Special Publication
811 should be used. There should always be a space between the numericalvalue and the unit symbol. The only exceptions to this are for the unit symbols
used for degree, minute and second for plane angle, º, ‘, “, respectively. Thismeans that there should never be a space between the degree symbol (º) when
it indicates a plane angle, e.g. 20º3’15’. However, there must always be a space
between the number and the unit symbol for degree Celsius, e.g., “20 ºC”
instead of “20ºC”, and between the numeric value and all other unit symbols.
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3.4.1.2. When multiple or sub-multiple prefixes are used, there is no space between
the prefix and the unit, e.g. kg, µV, mL, etc. Since lower case and upper caseprefixes indicate different multipliers, it is imperative that the correct case forthese prefixes be used, e.g. “kg”, not “Kg”; “mm”, not “MM”, etc. Please refer toSection 3 of the SI Brochure, 9th edition.
3.4.1.3. Expressions such as ppm (parts per million) must be avoided when
expressing uncertainty. Instead, ppm can be expressed as µV/V, µm/m, etc.,
or “parts per 106”3.4.2. The CMC uncertainty can never be zero (e.g. if range includes zero, uncertaintycannot be expressed as percent of reading/output alone, since this would result inan uncertainty of zero).
3.4.3. In certain cases, where a negative or zero quantity is not physically possible, “upto” may be used as the beginning of a range.
3.4.4. When expressing ranges, use the word “to” rather than the symbol “-“
3.4.5. The measurand or output range and the associated uncertainties provided in theCMC must be expressed in the same units. Exceptions can be made in rare
circumstances to avoid ambiguity. For example, in some cases the laboratory may
prefer to express electric power ranges as a combination of voltage and current, toindicate how the power is generated, while the uncertainty is expressed in units ofwatts or a multiple thereof.
3.4.6. For the specification of alternating current (AC) parameters on electrical scopes,
they have to be accompanied by either a fixed frequency or frequency range forwhich the stated uncertainty is valid. While there are many ways to accomplish thisin an unambiguous fashion, IAS chooses the following format:
MEASUREDQUANTITY or DEVICETYPE CALIBRATEDAC Voltage - Generate3RANGEUNCERTAINTY1,2(±)

1 mV to 200 mV(45 Hz to 1.999 kHz)
(2 kHz to 20 kHz)0.021 % + 56 µV
0.09 % + 0.23 mV

0.2 V to 20 V
(45 Hz to 1.999 kHz)
(2 kHz to 100 kHz)0.044 % + 0.3 mV
0.47 %+ 0.8 mV

20 V to 200 V(40 Hz to 1.999 kHz)
(2 kHz to 20 kHz)0.045 % + 15 mV
0.096 % + 17 mV

200 V to 750 V(40 Hz to 1 kHz)0.039 % + 104 mV

CALIBRATION METHOD OR
PROCEDURE, STANDARD
EQUIPMENT (OPTIONAL)
Using Multi product Calibrator
by direct method(IS 1248 - Part 9 (For Analogtype); IS 13875 - Part 1&2(For Digital type); CAT-CP-01(E))

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4. REFERENCES
BIPM, The International System of Units (SI), 9th ed.
IEEE/ASTM SI 10-2018: American National Standard for Metric PracticeILAC-G18:12/2021 Guideline for describing Scopes of Accreditation
ILAC-P14:9/2020 ILAC Policy for Uncertainty in Calibration
NIST SP 811, 2008 ed.: Guide for the Use of the International System of Units (SI)IAS/CL/022
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