SIST EN ISO 25178-606:2026

• Abstract:

  This document specifies the design and characteristics of focus variation instruments for areal measurement of surface topography. Because surface profiles can be extracted from areal surface topography data, the methods described in this document are also applicable to profiling measurements as well.; This document applies to focus variation without pattern illumination or with fixed pattern illumination. This document does not cover methods using varying pattern illumination during the measurement.

• Status: Published
• Public Enquiry End Date: 29-Apr-2025
• Publication Date: 15-Jun-2026
• ICS: 17.040.20 - Properties of surfaces
• ICS: 17.040.40 - Geometrical Product Specification (GPS)
• Technical Committee: ISEL - Mechanical elements
• Current Stage: 6060 - National Implementation/Publication (Adopted Project)
• Start Date: 02-Jun-2026
• Due Date: 07-Aug-2026
• Completion Date: 16-Jun-2026
• Ref Project: EN ISO 25178-606:2026 - Geometrical product specifications (GPS) - Surface texture: Areal - Part 606: Design and characteristics of non-contact (focus variation) instruments (ISO 25178-606:2026)

• Revises: SIST EN ISO 25178-606:2015 - Geometrical product specification (GPS) - Surface texture: Areal - Part 606: Nominal characteristics of non-contact (focus variation) instruments (ISO 25178-606:2015)
• Effective Date: 04-Oct-2023

SIST EN ISO 25178-606:2026 is the Slovenian adoption of EN ISO 25178-606:2026 for geometrical product specifications (GPS) surface texture, areal measurement. It specifies the design and characteristics of non-contact focus variation instruments used to measure surface topography, and it also applies to profiling measurements derived from areal data. The standard is aimed at instrument designers, metrology teams, and users who need to define, calibrate, or evaluate focus variation systems.

What does SIST EN ISO 25178-606:2026 specify?

SIST EN ISO 25178-606:2026 sets out the focus variation approach for areal measurement of surface topography. The scope covers focus variation without pattern illumination or with fixed pattern illumination, and it excludes varying pattern illumination during measurement.

The document is organized into seven clauses and three informative annexes.

Annex	What it covers
Annex A	Components of a focus variation instrument, its operating principle, illumination, scanner, objectives, algorithm, vibration, and limitations
Annex B	Sources of measurement error and how they relate to metrological characteristics
Annex C	Relationship to the GPS matrix model and the document's place in the GPS system

What are the key requirements of SIST EN ISO 25178-606:2026?

Instrument architecture and measurement chain

Clause 4 states that a focus variation instrument shall perform areal surface topography measurements using focus variation. The instrument shall include a focus variation sensor, optics, a focus variation illumination system, and an axial scanner.

Clause 4 also requires the instrument to collect data at several axial positions along the optical axis over an axial scan length. In practice, this means the instrument must create a stack of focus states and not just a single image, because height is derived from how the image sharpness changes during scanning.

The same clause requires the acquired data to be converted into areal topography by a focus variation measurement algorithm that calculates focus information and the focus information curve. For the user, this defines the core software function: the instrument is not complete unless it can turn the scan data into topography.

Illumination, detection, and polarization

Clause 4 describes the illumination and detection geometry. The surface is illuminated over an angular range of illumination, and data are captured over an angular range of detection. This matters because illumination geometry affects which surfaces can be measured well, especially steep or reflective ones.

Clause 4 also notes that polarization mode can help with specular reflection. A polarizer and an analyser are used for that purpose. In practice, that means the instrument design may need optical elements to reduce unwanted reflected light from shiny surfaces.

Metrological characteristics and calibration

Clause 5 states that the metrological characteristics in ISO 25178-600 shall be considered when designing and calibrating the instrument. This links the instrument design to the properties that matter in measurement practice, such as noise, spatial resolution, flatness deviation, linearity deviation, and mapping behavior.

Annex B explains the main influence quantities behind those characteristics. It identifies, among others, light sources, numerical aperture, instrument noise, environmental vibration, optical lateral resolution, sampling interval, optical distortion, and the axial scan system. For a buyer or lab, this is the list to check when comparing instruments or investigating measurement error.

Design features and practical limits

Clause 6 says the standard design features in ISO 25178-600 shall be considered in the design. Annex A then gives examples of how focus variation instruments are built, including the typical configuration, objectives, illumination options, and scanning methods.

Annex A also explains where focus variation works well and where it is limited. It describes the need for sufficient focus variation in the image data and notes that fixed pattern illumination can extend measurability to optically smooth surfaces. In practice, this means surface reflectivity and texture need to match the chosen illumination concept.

Position in the GPS system

Clause 7 and Annex C place this document in the GPS matrix model. The standard is a general GPS standard and influences chain link F for profile and areal surface texture. For users of GPS specifications, this shows that the document belongs to the measurement and verification part of the system, not the feature-definition part.

What terms does SIST EN ISO 25178-606:2026 define?

• Focus variation (FV) - A measurement method that uses the sharpness of a series of surface images collected during an axial scan to determine surface topography.
• Focus variation sensor - A device that converts surface height into signals during measurement using the focus variation method.
• Axial scan - The mechanical or optical displacement between the sample and the imaging optics during data acquisition.
• Focus information curve - The signal for one lateral position plotted against axial scan position, showing where the point is best in focus.
• Angular range of illumination - The range of angles from which the sample is illuminated; it affects the measurable slope on optically smooth surfaces.
• Polarization mode - A method for filtering light by polarization state using a polarizer or an analyser.

Who uses SIST EN ISO 25178-606:2026?

SIST EN ISO 25178-606:2026 is used by designers of optical surface metrology instruments, especially focus variation microscopes and sensors. It is also used by calibration and verification laboratories that need to relate instrument performance to the metrological characteristics in ISO 25178-600.

Quality engineers, inspection teams, and manufacturing buyers use it when they need to specify or assess 3D surface topography measurement capability. It is relevant in production environments where surface texture, reflectance, slope, vibration sensitivity, and scan behavior affect the measurement result.

What changed in SIST EN ISO 25178-606:2026 from the previous edition?

This second edition supersedes the first edition. The stated changes are:

• removal of terms and definitions that are now given in ISO 25178-600
• revision of all terms and definitions for clarity and consistency with other ISO standards
• addition of Clause 4 on instrument requirements
• addition of Clause 5 on metrological characteristics
• addition of Clause 6 on design features
• addition of an information flow concept diagram in Clause 4
• revision of Annex A on focus variation principles and instrument components
• addition of Annex B on metrological characteristics and influence quantities, replacing the former normative table of influence quantities with an informative description

Which standards are used with SIST EN ISO 25178-606:2026?

• ISO 25178-600:2019 - supplies the metrological characteristics for areal topography measuring methods and the design features referred to in Clauses 5 and 6.
• ISO 8015 - provides the fundamental GPS rules that apply to this document.
• ISO 14253-1 - provides the default decision rules for verifying conformity or nonconformity with specifications.
• ISO 14638 - provides the GPS matrix model used to place this document in the GPS system.
• ISO 25178-700 - gives calibration, adjustment, and verification methods for areal topography measuring instruments.
• ISO 25178-603 - is a related non-contact areal surface texture standard, and the document notes that some influence-quantity definitions are the same.
• ISO 25178-607:2019 - is the confocal microscopy part of the series and is cited for related scan terminology and source definitions.

What does the SIST EN ISO 25178-606:2026 document contain?

The document contains the scope, normative references, terms and definitions, instrument requirements, metrological characteristics, design features, and general information. It also includes an information flow concept diagram that shows how focus variation data move from the measured surface to the calculated topography.

Annex A contains a schematic of a typical focus variation instrument, examples of illumination systems, scanner approaches, objective characteristics, and focus-curve evaluation methods. It also includes a step-height example and a discussion of practical limits such as surface roughness, smooth surfaces, and vibration.

Annex B summarizes error sources and links them to metrological characteristics such as topographic spatial resolution, measurement noise, flatness deviation, mapping deviation, and linearity deviation. Annex C explains the document's role in the GPS matrix model and its chain-link position for profile and areal surface texture.

SLOVENSKI STANDARD
01-julij-2026
Specifikacija geometrijskih veličin izdelka (GPS) - Tekstura površine: ploskovna -
606. del: Načrtovanje in značilnosti brezkontaktnih instrumentov (sprememba
ostrine) (ISO 25178-606:2026)
Geometrical product specifications (GPS) - Surface texture: Areal - Part 606: Design and
characteristics of non-contact (focus variation) instruments (ISO 25178-606:2026)
Geometrische Produktspezifikation (GPS) - Oberflächenbeschaffenheit: Flächenhaft -
Teil 606: Aufbau und Merkmale von berührungslos messenden Geräten (Fokusvariation)
(ISO 25178-606:2026)
Spécification géométrique des produits (GPS) - État de surface: Surfacique - Partie 606:
Conception et caractéristiques des instruments sans contact (à variation de focale) (ISO
25178-606:2026)
Ta slovenski standard je istoveten z: EN ISO 25178-606:2026
ICS:
17.040.20 Lastnosti površin Properties of surfaces
17.040.40 Specifikacija geometrijskih Geometrical Product
veličin izdelka (GPS) Specification (GPS)
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN ISO 25178-606
EUROPEAN STANDARD
NORME EUROPÉENNE
May 2026
EUROPÄISCHE NORM
ICS 17.040.40 Supersedes EN ISO 25178-606:2015
English Version
Geometrical product specifications (GPS) - Surface texture:
Areal - Part 606: Design and characteristics of non-contact
(focus variation) instruments (ISO 25178-606:2026)
Spécification géométrique des produits (GPS) - État de Geometrische Produktspezifikation (GPS) -
surface: Surfacique - Partie 606: Conception et Oberflächenbeschaffenheit: Flächenhaft - Teil 606:
caractéristiques des instruments sans contact (à Aufbau und Merkmale von berührungslos messenden
variation de focale) (ISO 25178-606:2026) Geräten (Fokusvariation) (ISO 25178-606:2026)
This European Standard was approved by CEN on 23 April 2026.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this
European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references
concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN
member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by
translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management
Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and
United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2026 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 25178-606:2026 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
This document (EN ISO 25178-606:2026) has been prepared by Technical Committee ISO/TC 213
"Dimensional and geometrical product specifications and verification" in collaboration with Technical
Committee CEN/TC 290 “Dimensional and geometrical product specification and verification” the
secretariat of which is held by AFNOR.
This European Standard shall be given the status of a national standard, either by publication of an
identical text or by endorsement, at the latest by November 2026, and conflicting national standards
shall be withdrawn at the latest by November 2026.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
This document supersedes EN ISO 25178-606:2015.
Any feedback and questions on this document should be directed to the users’ national standards
body/national committee. A complete listing of these bodies can be found on the CEN website.
According to the CEN-CENELEC Internal Regulations, the national standards organizations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,
Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland,
Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of
North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and the
United Kingdom.
Endorsement notice
The text of ISO 25178-606:2026 has been approved by CEN as EN ISO 25178-606:2026 without any
modification.
International
Standard
ISO 25178-606
Second edition
Geometrical product specifications
2026-05
(GPS) — Surface texture: Areal —
Part 606:
Design and characteristics of
non-contact (focus variation)
instruments
Spécification géométrique des produits (GPS) — État de surface:
Surfacique —
Partie 606: Conception et caractéristiques des instruments sans
contact (à variation de focale)
Reference number
ISO 25178-606:2026(en) © ISO 2026

ISO 25178-606:2026(en)
© 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
ISO 25178-606:2026(en)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Instrument requirements . 5
5 Metrological characteristics . 6
6 Design features . 6
7 General information . 6
Annex A (informative) Components of a focus variation instrument . 7
Annex B (informative) Sources of measurement error for focus variation . 14
Annex C (informative) Relationship to the GPS matrix model . 17
Bibliography .18

iii
ISO 25178-606:2026(en)
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
ISO technical committees. Each member body interested in a subject for which a technical committee
has been established has the right to be represented on that committee. International organizations,
governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely
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)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions
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 213, Dimensional and geometrical product
specifications and verification, in collaboration with the European Committee for Standardization (CEN)
Technical Committee CEN/TC 290, Dimensional and geometrical product specification and verification, in
accordance with the Agreement on technical cooperation between ISO and CEN (Vienna Agreement).
This second edition cancels and replaces the first edition (ISO 25178:606:2015), which has been technically
revised.
The main changes are as follows:
— removal of the terms and definitions now specified in ISO 25178-600;
— revision of all terms and definitions for clarity and consistency with other ISO standards documents;
— addition of Clause 4 for instrument requirements;
— addition of Clause 5 on metrological characteristics;
— addition of Clause 6 on design features, which clarifies the types of instruments relevant to this document;
— addition of an information flow concept diagram in Clause 4;
— revision of Annex A describing the principles of instruments addressed by this document;
— addition of Annex B on metrological characteristics and influence quantities, replacement of the
normative table of influence quantities with an informative description of common error sources and
how these relate to the metrological characteristics in ISO 25178-600.
A list of all parts in the ISO 25178 series can be found on the ISO website.
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
ISO 25178-606:2026(en)
Introduction
This document is a geometrical product specification (GPS) standard and is to be regarded as a general GPS
standard (see ISO 14638). It influences the chain link F of the chain of standards on profile and areal surface
texture.
The ISO GPS matrix model given in ISO 14638 gives an overview of the ISO GPS system of which this
document is a part. The fundamental rules of ISO GPS given in ISO 8015 apply to this document and the
default decision rules given in ISO 14253-1 apply to specifications made in accordance with this document,
unless otherwise indicated.
For more detailed information of the relation of this document to other standards and the GPS matrix model,
see Annex C.
This document includes terms and definitions relevant to the focus variation instruments for the
measurement of areal surface topography. Annex A briefly summarizes focus variation instruments and
methods to clarify the definitions and to provide a foundation for Annex B, which describes common sources
of uncertainty and their relation to the metrological characteristics of focus variation.
NOTE Portions of this document, particularly the informative sections, describe patented systems and methods.
This information is provided only to assist users in understanding the operating principles of focus variation. This
document is not intended to establish priority for any intellectual property, nor does it imply a license to proprietary
technologies described herein.

v
International Standard ISO 25178-606:2026(en)
Geometrical product specifications (GPS) — Surface texture:
Areal —
Part 606:
Design and characteristics of non-contact (focus variation)
instruments
1 Scope
This document specifies the design and characteristics of focus variation instruments for areal measurement
of surface topography. Because surface profiles can be extracted from areal surface topography data, the
methods described in this document are also applicable to profiling measurements as well.
This document applies to focus variation without pattern illumination or with fixed pattern illumination.
This document does not cover methods using varying pattern illumination during the measurement.
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 25178-600:2019, Geometrical product specifications (GPS) — Surface texture: Areal — Part 600:
Metrological characteristics for areal topography measuring methods
3 Terms and definitions
For the purposes of this document, the following terms and definitions 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
focus variation
FV
measurement method whereby the sharpness of a series of surface images that is acquired during an axial
scan in an optical instrument is used to measure the surface topography
Note 1 to entry: In this document, surface image is an image of a surface obtained by capturing the reflected light from
the surface with or without a fixed pattern illumination.
Note 2 to entry: In this document, sharpness is a quantity of the surface image calculated by the neighbourhood
information indicating best focus. Other names for sharpness are for example contrast.
Note 3 to entry: Focus variation without fixed pattern illumination only works on optically rough surfaces (see
ISO 25178-600:2019, 3.4.5). If fixed pattern illumination is used, optically smooth surfaces (see ISO 25178-600:2019,
3.4.4) can also be measured.
ISO 25178-606:2026(en)
3.2
focus variation sensor
device that converts the height of points on the surface into signals during measurement using the focus
variation (3.1) method
3.3
axial scan
mechanical or optical displacement between the sample under inspection and the imaging optics
Note 1 to entry: The optical axis of the imaging optics is nominally parallel to the axial scan axis of the microscope.
[SOURCE: ISO 25178-607:2019, 3.5, modified — “imaging optics” replaced by “optical axis of the imaging
optics” in Note 1 to entry.]
3.4
focus variation measurement algorithm
algorithm for analysing the variation of focus in order to calculate the scan positions where each point is
best in focus
3.5
focus information
measure to quantify the degree of focus based on image sharpness at a specific lateral position in the surface
image and at a specific axial scan (3.3) position
3.6
focus information curve
signal recorded for a specific lateral position of the surface image as a function of the axial scan (3.3) position
Note 1 to entry: See Figure 1.
Note 2 to entry: The surface is located at the axial scan position of the maximum of the focus information curve (see
"1" in Figure 1).
Note 3 to entry: To improve the resolution in axial scan direction, the maximum of a fitted curve can be used instead
of "1" in Figure 1.
Key
X axial scan position
Y focus information
1 highest focus information from the captured axial scan positions
Figure 1 — Focus information curve

ISO 25178-606:2026(en)
3.7
focus variation illumination system
source of light with a predefined spectral and spatial distribution
Note 1 to entry: Possible light sources are coaxial illumination, ring light and external light sources.
Note 2 to entry: A variant of coaxial illumination is the use of a fixed pattern projected onto a sample surface. For
example, this pattern can be a chessboard.
3.8
angular range of illumination
α
angular range from which the sample is illuminated
Note 1 to entry: See Figure 2.
Note 2 to entry: The angular range of illumination affects the maximum measurable slope on optically smooth
surfaces.
3.8.1
angular range of coaxial illumination
α
I
angular range from which the sample is coaxially illuminated
Note 1 to entry: The value α can be influenced by the choice of the objective.
I
Note 2 to entry: The value α is often related to the angular range of detection, see Figure 3.
I
Note 3 to entry: In normal cases, the value α can be derived from the numerical aperture of the objective.
I
Note 4 to entry: When special illumination sources are used (ring light, external light sources, etc., see Figure 2) the
angular range of illumination (3.8) can be much larger than α .
I
3.8.2
minimum incident angle of ring light illumination
β
Imin
angle between the optical axis and the light rays of the ring light that illuminate the sample closest to the
optical axis
Note 1 to entry: See Figure 2.
3.8.3
maximum incident angle of ring light illumination
β
Imax
angle between the optical axis and the light rays of the ring light that illuminate the sample farthest to the
optical axis
Note 1 to entry: See Figure 2.

ISO 25178-606:2026(en)
Key
L lens of optical system
RL ring light
α angular range of coaxial illumination
I
β minimum incident angle of ring light illumination
Imin
β maximum incident angle of ring light illumination
Imax
S sample
Figure 2 — Angular range of illumination
3.9
angular range of detection
α
D
angular range of light rays that can be gathered by the objective
Note 1 to entry: See Figure 3.
Key
L lens of optical system
RL ring light
α angular range of detection
D
S sample
Figure 3 — Angular range of detection

ISO 25178-606:2026(en)
3.10
axial scan length
total range travelled by the focus variation microscope axial scan (3.3), usually the total displacement
between the sample and the microscope’s objective translated along its optical axis during data acquisition
Note 1 to entry: This parameter can be limited by the overall range of the axial scanner, but is generally a parameter
chosen by the operator taking account of the height range of the surface topography.
[SOURCE: ISO 25178-607:2019, 3.6, modified —“confocal microscope axial scan” has been replaced by “focus
variation microscope axial scan”.]
3.11
polarization mode
method which allows one to filter out light waves in certain polarization states by using special optical
elements called polarizers (3.13) or analysers (3.12)
3.12
analyser
optical element used to filter the rays of the light after they have been reflected from the sample and
gathered by the objective before reaching the electronic camera
3.13
polarizer
optical element used to polarize the rays of the light source before they are transmitted to the sample
4 Instrument requirements
An instrument shall perform areal surface topography measurements of a sample surface using focus
variation. The instrument shall comprise a focus variation sensor, optics, focus variation illumination
system, and an axial scanner. The instrument shall acquire data by illuminating the surface with an angular
range of illumination and capturing data from angular range of detection at several axial positions along the
optical axis by performing an axial scan over an axial scan length. To improve the performance of specular
reflection the application of polarization mode can help. Therefore, a polarizer and an analyser are used.
The instrument shall convert acquired data to an areal topography using a focus variation measurement
algorithm which calculates the focus information to get the focus information curve.
Figure 4 shows the information flow between these elements for a FV instrument, from the real surface
to a scale-limited surface. Example FV hardware, techniques and error sources are given in Annex A and
Annex B.
ISO 25178-606:2026(en)
Key
measurand
operator with intended modification
operator without intended modification
Figure 4 — Information flow concept diagram for focus variation instruments
5 Metrological characteristics
The standard metrological characteristics for areal surface texture measuring instruments specified in
ISO 25178-600 shall be considered when designing and calibrating the instrument.
Annex B describes sources of measurement error that can influence the calibration result.
6 Design features
Standard design features specified in ISO 25178-600 shall be considered in the design.
Annex A provides examples of specific design features of FV instruments.
7 General information
The relation between this document and the GPS matrix model is given in Annex C.

ISO 25178-606:2026(en)
Annex A
(informative)
Components of a focus variation instrument
A.1 General
This annex is a short overview of the focus variation principle and the components of a focus variation
instrument. Further literature can be found in References [8] to [24].
A.2 Typical c
...