ISO 27893:2026

• Abstract:

  This document specifies a method for the determination and reporting of measurement uncertainties arising during vacuum gauge calibration by direct comparison with a reference gauge carried out in accordance with ISO 3567. This document specifies methods for uniform reporting of uncertainties in vacuum gauge certificates. Uncertainties reported in accordance with the guidelines given in this document are transferable in the sense that the uncertainty evaluated for one result can be used as a component in the uncertainty evaluation of another measurement or calibration in which the first result is used. This document specifies two measurement models that are sufficient to cover most practical cases. However, it is possible that the models given cannot be applied to newly developed vacuum gauges. The final uncertainty to be reported in a certificate is evaluated from the uncertainties of the input quantities and influence quantities. The principal quantities that can affect the result of a vacuum calibration are described; however, a complete list of the possible quantities that can have an influence on the final result lies outside the scope of this document.

• Status: Published
• Publication Date: 27-Jul-2026
• ICS: 23.160 - Vacuum technology
• Technical Committee: ISO/TC 112 - Vacuum technology
• Drafting Committee: ISO/TC 112 - Vacuum technology
• Current Stage: 6060 - International Standard published
• Start Date: 28-Jul-2026
• Due Date: 30-Aug-2026
• Completion Date: 28-Jul-2026

• Revises: ISO 27893:2011 - Vacuum technology — Vacuum gauges — Evaluation of the uncertainties of results of calibrations by direct comparison with a reference gauge
• Effective Date: 29-Oct-2022

Overview

ISO 27893:2026 is an international standard developed by ISO focusing on the evaluation and reporting of measurement uncertainties in vacuum gauge calibration. It provides methodologies for determining the uncertainties that arise during calibrations performed by direct comparison with a reference gauge, following procedures set forth in ISO 3567. ISO 27893:2026 establishes consistent approaches for uncertainty calculation and reporting in calibration certificates, helping ensure traceability and comparability across laboratories and industries engaged in vacuum technology.

Uniform reporting of uncertainties as prescribed by this standard allows results to be transferable. That is, uncertainty evaluations from one calibration can be incorporated as components in subsequent measurements, streamlining quality assurance and compliance activities related to vacuum equipment.

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Key Topics

• Measurement Models:
  The standard introduces two primary models for uncertainty evaluation:

  • Sum Model: Used when the difference between the unit under calibration (UUC) reading and the reference pressure is the measurand (e.g., error of reading).
  • Quotient Model: Used when the relationship between readings is expressed as a ratio (e.g., correction factors, sensitivity coefficients).
  • Model Combination: Guidance is provided for scenarios requiring a combination of both models, especially for assessing the error of reading.

• Uncertainty Contributions:
  The uncertainty components considered include:

  • Reference gauge characteristics (offsets, drift, calibration, environmental influences)
  • The vacuum gauge under calibration (repeatability, stability, environmental effects)
  • Calibration method and conditions (temperature gradients, pressure differentials, measurement procedure)

• Uncertainty Reporting:
  ISO 27893:2026 outlines:

  • Construction of uncertainty budgets
  • Issuance of calibration certificates with standardized uncertainty statements
  • Procedures for selecting coverage factors, ensuring proper confidence levels

• Transferability of Data:
  Results and corresponding uncertainties, when reported according to this standard, can be reused as valid input for future calibrations, increasing the efficiency and consistency of measurement traceability.

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Applications

The practical value of ISO 27893:2026 spans several critical areas in vacuum technology and calibration services:

• Vacuum Gauge Calibration Laboratories:
  Ensures consistency and reliability in issuing vacuum gauge calibration certificates by direct comparison, supporting traceability to SI units.

• Quality Assurance in Manufacturing:
  Enables manufacturers of scientific and industrial equipment (such as semiconductor fabrication, vacuum coating, or analytical laboratories) to comply with internationally recognized calibration protocols, minimizing uncertainties in process control.

• Research and Development:
  Research labs specializing in low-pressure science and technology benefit from robust methods to quantify and minimize measurement uncertainties in vacuum instrumentation.

• Traceability and Regulatory Compliance:
  Calibration results and certificates aligned with ISO 27893:2026 support global regulatory and quality system requirements, such as those demanded in ISO/IEC 17025-accredited calibration laboratories.

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Related Standards

• ISO 3567: Vacuum gauges - Calibration by direct comparison with a reference gauge
  Defines the procedures referenced in ISO 27893:2026 for performing the direct comparison calibration.

• ISO/IEC Guide 98-3 (GUM 1995): Guide to the Expression of Uncertainty in Measurement
  Provides foundational principles for the evaluation and expression of measurement uncertainty used throughout ISO 27893:2026.

• ISO/IEC Guide 99:2007 (VIM): International Vocabulary of Metrology
  Standardizes terminology in metrology, supporting clear and consistent uncertainty reporting.

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By following ISO 27893:2026, organizations involved in vacuum gauge calibration can achieve uniformity, traceability, and comparability in their measurement uncertainty evaluations-driving higher quality standards within the vacuum technology sector.

International
Standard
ISO 27893
Second edition
Vacuum technology — Vacuum
2026-07
gauges — Evaluation of the
uncertainties of results of
calibrations by direct comparison
with a reference gauge
Technique du vide — Manomètres à vide — Évaluation de
l'incertitude des résultats des étalonnages par comparaison
directe avec un manomètre de référence
Reference number
© ISO 2026
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and abbreviated terms. 3
5 Basic concept and model . 3
5.1 General .3
5.2 Sum model .4
5.3 Quotient model .4
5.4 Combination of the two models .5
6 Calculation of uncertainty in the sum model . 5
6.1 Total uncertainty — Sum model .5
6.2 Uncertainty contributions due to reference standard .5
6.3 Uncertainty contributions due to unit under calibration .7
6.4 Uncertainty contributions due to calibration method or calibration conditions .8
6.5 Coverage factor .8
7 Calculation of uncertainty in the quotient model . 8
7.1 Total uncertainty — Quotient model .8
7.2 Uncertainty contributions due to reference standard .9
7.3 Uncertainty contributions due to the unit under calibration .10
7.4 Uncertainty contributions due to calibration method or calibration conditions .11
7.5 Coverage factor . 12
8 Combination of the sum and quotient model for error of reading.12
9 Reporting uncertainties .13
9.1 Uncertainty budget . 13
9.2 Calibration certificate .14
Annex A (normative) Efficient uncertainty analysis when Type A uncertainties are not
negligible .15
Bibliography . 17

iii
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
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has been established has the right to be represented on that committee. International organizations,
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with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types
of ISO document should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
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this may not represent the latest information, which may be obtained from the patent database available at
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related to conformity assessment, as well as information about ISO's adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 112, Vacuum technology.
This second edition cancels and replaces the first edition (ISO 27893:2011), which has been technically
revised.
The main changes are as follows:
— added Annex A, which describes how to evaluate Type A uncertainties.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.

iv
International Standard ISO 27893:2026(en)
Vacuum technology — Vacuum gauges — Evaluation of the
uncertainties of results of calibrations by direct comparison
with a reference gauge
1 Scope
This document specifies a method for the determination and reporting of measurement uncertainties arising
during vacuum gauge calibration by direct comparison with a reference gauge carried out in accordance
with ISO 3567.
This document specifies methods for uniform reporting of uncertainties in vacuum gauge certificates.
Uncertainties reported in accordance with the guidelines given in this document are transferable in the
sense that the uncertainty evaluated for one result can be used as a component in the uncertainty evaluation
of another measurement or calibration in which the first result is used.
This document specifies two measurement models that are sufficient to cover most practical cases. However,
it is possible that the models given cannot be applied to newly developed vacuum gauges.
The final uncertainty to be reported in a certificate is evaluated from the uncertainties of the input quantities
and influence quantities. The principal quantities that can affect the result of a vacuum calibration are
described; however, a complete list of the possible quantities that can have an influence on the final result
lies outside the scope of this document.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes
requirements of this document. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
ISO 3567, Vacuum gauges — Calibration by direct comparison with a reference gauge
ISO/IEC Guide 98-3, Uncertainty of measurement — Part 3: Guide to the expression of uncertainty in
me a s ur ement (GUM: 1995)
ISO/IEC Guide 99:2007, International vocabulary of metrology — Basic and general concepts and associated
terms (VIM)
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 3567, ISO/IEC Guide 98-3,
ISO/IEC Guide 99 and the following apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
corrected reading
value resulting after the reading of the gauge has been corrected for systematic errors
EXAMPLE For the results given in the calibration certificate of the reference standard.

3.2
long-term instability
possible change of calibrated value after long periods of time
EXAMPLE Change resulting from transportation of the device.
Note 1 to entry: Long-term instability is different from reproducibility as defined in ISO/IEC Guide 99:2007, 3.7.
3.3
model
〈uncertainty of measurement〉 mathematical model set out in ISO/IEC Guide 98-3
3.4
offset
zero error
〈measuring instruments〉 datum measurement error where the specified measured quantity value is zero
Note 1 to entry: Adapted from ISO/IEC Guide 99:2007, 4.28.
EXAMPLE The reading when there is no pressure (absolute or differential) or a pressure far below the resolution
limit applied to a vacuum gauge.
3.5
deviation of offset
possible difference of an offset (3.4) value between the time of the measurement of the offset (3.4) and the
time when a pressure reading is taken
3.6
reference standard
reference gauge
standard, generally having the highest metrological quality available at a given location or in a given
organization, from which measurements made there are derived
Note 1 to entry: Adapted from ISO/IEC Guide 99:2007, 6.6.
EXAMPLE The gauge or standard that gives traceability to the SI unit in the calibration apparatus in accordance
with ISO 3567.
3.7
calibration pressure
〈vacuum gauges〉 pressure evaluated from the corrected reading (3.1) of the reference standard (3.6) and all
necessary corrections at the gauge port of the unit under calibration
EXAMPLE Necessary corrections can be for known differences between gauge ports.
3.8
Type A and Type B uncertainties
classifications used to indicate the two different ways of evaluating uncertainty components, which are
intended only for convenience of discussion
Note 1 to entry: The classification is not meant to indicate any difference in the nature of the uncertainty components.
Note 2 to entry: Type A uncertainties are evaluated by the statistical analysis of series of observations.
Note 3 to entry: Type B uncertainties are evaluated by means other than the statistical analysis of series of
observations.
Note 4 to entry: For more information, see ISO/IEC Guide 98-3.

4 Symbols and abbreviated terms
Symbol or Designation Unit
abbreviated term
UUC unit under calibration (vacuum gauge) —
e error of reading in relative units
k coverage factor to expand standard uncertainty, u 1
p pressure indication of a UUC corrected for known deviations Pa
UUC
p pressure indication of a UUC not corrected for any deviation Pa
ind,UUC
p pressure indication of reference gauge (reference standard) Pa
std
corrected for known deviations
p pressure indication of reference gauge (reference standard) not Pa
ind,std
corrected for any deviation
r quantity determined by a calibration in the quotient model for the any unit
UUC
UUC
r quantity determined by a calibration in the quotient model for the any unit
std
reference standard
S sensitivity of the output of a vacuum gauge any unit
u standard uncertainty any unit
U expanded uncertainty any unit
x indication of a UUC any unit
UUC
x indication of a reference gauge any unit
std
x (often unknown) input quantities and corrections of gauge any unit
i
X (often unknown) input quantities and corrections of calibration any unit
i
method or condition
Δp error of pressure reading in absolute units Pa
δp deviations in the pressure unit (often unknown) Pa
i
δx (often unknown) deviations in x any unit
i i
σ effective accommodation factor of a spinning rotor gauge 1
eff
5 Basic concept and model
5.1 General
In a vacuum gauge calibration carried out in accordance with ISO 3567, the corrected reading of a reference
gauge gives the value of the quantity that is traceable to the SI. All vacuum gauges shall be calibrated in
terms of pressure. This means that the user of the vacuum gauge calibrated in accordance with ISO 3567 and
this document obtains a clear assignment of the output quantity of the gauge to the SI unit of pressure, the
pascal.
The value of pressure obtained from the corrected reading of the reference standard output can be used
to determine the pressure at the entrance port of the unit under calibration (UUC). This is referred to
as calibration pressure value. Often the corrected reading of the reference standard is identical to the
calibration pressure value and valid for all gauge ports.
The calibration pressure value can be used to determine an error of the reading, Δp, of the unit under
calibration. In this case, a sum model gives an adequate description of the measurement.
The calibration pressure value can also be used to determine a correction factor, a sensitivity coefficient,
an effective accommodation factor or a gauge constant, in which case a quotient model gives an adequate
description of the measurement.
In both models it can be assumed that all the input quantities are uncorrelated.
5.2 Sum model
In the sum model, the difference between the reading of the UUC, p , and the “true” calibration pressure
UUC
traceable to the SI units is taken as the measurand, Δp. The calibration pressure is given by the reference
standard pressure value, p , and possibly by a correction term, δp , due to the calibration method
std m
considering known effects like height correction, thermal transpiration, and pressure non-uniformity. The
general sum model thus becomes
pp pp � (1)

UUC stdm
The first term refers to the UUC, the second to the reference standard, and the third to the calibration
method. The sum of the last two terms gives the calibration pressure value. All quantities shall be expressed
in the SI unit of pressure, the pascal.
Each of these terms is again expressed by another model equation, which makes all necessary corrections
due to offsets, temperature corrections, deviation of indication from the SI value in accordance with the
calibration certificate, etc.
5.3 Quotient model
In the quotient model, the ratio of the reading of the UUC, x , and the standard pressure value, p , is
UUC std
taken as the measurand, r . The general quotient model thus becomes
UUC
x
UUC
r  X � (2)
UUC  i
p
std
i
The numerator refers to the UUC, the denominator to the reference standard, and the product to the
calibration method and conditions. The latter can also be defined by the vacuum gauges under calibration,
e.g. the emission current in a hot cathode ionization gauge. It is possible to express x in any reasonable
UUC
unit, e.g. that of pressure, voltage or current. The X can be expressed in any meaningful physical unit or can
i
be without dimension.
Each of these factors is expressed by another model equation, which makes all necessary corrections due to
offsets, temperature corrections, deviation of indication in accordance with calibration certificate, etc.
Examples of r are
UUC
-1
a) f the reciprocal of a dimensionless correction factor, where x = p and X = 1;
c UUC UUC i
b) S a sensitivity of the analogue output, V , of a capacitance diaphragm gauge, where x = V ;
UUC UUC UUC
c) S a sensitivity of the analogue output, V , of a thermal conductivity gauge, where x = V ;
UUC UUC UUC
d) σ the effective accommodation factor of a spinning rotor gauge, where x = p , when σ = 1 was
eff UUC UUC eff
entered into the controller;
e) S a sensitivity of a Bayard-Alpert gauge with a hot cathode, where x = I is the positive ion current
UUC UUC
of the collector and X = 1/I , where I is the emission current.
1 e e
5.4 Combination of the two models
It is possible to evaluate some of the input quantities in each model by either of the two models. First, for
example, p as well as its uncertainty can be evaluated by the quotient model, thus
std
x
std
p = � (3)
std
r
std
The result can then be used in Formula (1). This is unavoidable if r is given in the certificate applying
std
Formula (2) (e.g. the sensitivity of an analogue output), where r is replaced by r .
UUC std
It is, however, not recommended to combine the sum and quotient model in one Formula. This task should be
left to experts, since complicated sensitivity coefficients can appear that are not covered in this document
for reasons of clarity. The relative error of reading, e, however, is a common case, where an easy-to-handle
combination of the two methods is possible.
The error of reading, e, can be expressed mathematically as
ppp p

UUC stdm UUC
e   1� (4)
pppp

stdm stdm
or, if δp = 0
m
pp p
UUC std UUC
e 1� (5)
p p
std std
See Clause 4 for the designations of p , p , and δp . The uncertainty of e is described in Clause 8.
UUC std m
6 Calculation of uncertainty in the sum model
6.1 Total uncertainty — Sum model
The total uncertainty in the sum model, u(Δp), is given by
22 2
up  up up up � (6)
   
UUC stdm
where
u(p ) is the standard uncertainty of the corrected pressure indication of the vacuum gauge under
UUC
calibration;
u(p ) is the standard uncertainty of the corrected pressure indication of the reference gauge;
std
u(δp ) is the standard uncertainty of the deviations due to the calibration method.
m
6.2 Uncertainty contributions due to reference standard
The corrected pressure indication of the reference standard p is given by
std
ppppp 
stdind,,stdoffs stddrfts,,td calstd
(7)
pp pp
term,std TT,,stdthermal stdels,std
where
p is the indication of the reference standard;
ind,std
p is the offset (zero deviation) of the reference standard;
offs,std
δp is the deviation of offset due to drift (in most cases, δp = 0);
drft,std drft,std
δp is the correction in accordance with the calibration certificate;
cal,std
δp is the deviation due to long-term instability (in most cases, δp = 0);
term,std term,std
δp is the deviation due to temperature at the calibration laboratory;
T,std
p is the deviation due to the effect of thermal transpiration caused by the temperature difference
thermal,std
between reference standard and the unit under calibration;
δp is the deviation due to other influences, e.g. inclination of device (in most cases, δp = 0).
els,std els,std
All quantities in Formula (7) refer to the reference standard gauge.
NOTE If the offset is deducted or adjusted to zero in the device itself, p = 0.
offs,std
The standard uncertainty of the corrected pressure indication of the reference standard u(p ) then is
std
given by
22 2 2
up up upup 
   
ind,stdoffs,std drft,std cal,sttd
up  � (8)

std
22 2 2
upup up up
   
term,std T,stdthermal,std els,sstd
where
u(p ) is the uncertainty originating from the dispersion of measurement values, including
ind,std
dispersion due to digitizing, resolution scatter, etc.;
u(p ) is the uncertainty of the offset values at measurement of the offset [without reproduc-
offs,std
ibility of the offset covered by u(δp )];
drft,std
u(δp ) is the uncertainty of the offset values at time of calibration due to offset drift or other
drft,std
systematic dependencies, e.g. due to the frequency dependence of spinning rotor gauges;
u(δp ) is the uncertainty of the standard in accordance with the calibration certificate;
cal,std
u(δp ) is the uncertainty component of the long-term instability;
termstd
u(δp ) is the uncertainty component due to the temperature influence under the conditions of
T,std
the calibration laboratory;
u(p ) is the uncertainty component due to the effect of thermal transpiration caused by the
thermal,std
temperature difference between the reference standard and the unit under calibration;
u(δp ) is the uncertainty due to the specific conditions at the calibration laboratory, e.g. dif-
els,std
ferent mounting position of built-in devices.
For a p that has not been obtained from repeated observations, estimate u(p ) from scientific
ind,std ind,std
judgement based on all of t
...