ISO 9241-4:1998

INTERNATIONAL ISO
STANDARD 9241-4
First edition
1998-08-01
Ergonomic requirements for office work
with visual display terminals (VDTs) —
Part 4:
Keyboard requirements
Exigences ergonomiques pour travail de bureau avec terminaux à écrans
de visualisation (TEV) —
Partie 4: Exigences relatives aux claviers
A
Reference number
ISO 9241-4:1998(E)

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ISO 9241-4:1998(E)
Contents Page
1 Scope . 1
2 Normative references . 1
3 Definitions . 2
4 Guiding principles . 7
Performance criterion .
5 8
6 Design requirements and recommendations. 8
7 Measurement. 13
8 Conformance . 19
Annex
Usability test (proposed alternative test) .
A 20
B Bibliography . 27
©  ISO 1998
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced
or utilized in any form or by any means, electronic or mechanical, including photocopying and
microfilm, without permission in writing from the publisher.
International Organization for Standardization
Case postale 56 • CH-1211 Genève 20 • Switzerland
Internet iso@iso.ch
Printed in Switzerland
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ISO ISO 9241-4:1998(E)
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.
Draft International Standards adopted by the technical committees are
circulated to the member bodies for voting. Publication as an International
Standard requires approval by at least 75 % of the member bodies casting
a vote.
International Standard ISO 9241-4 was prepared by the Technical
Committee ISO/TC 159, Ergonomics, Subcommittee SC 4, Ergonomics of
human system interaction.
ISO 9241 consists of the following parts, under the general title Ergonomic
requirements for office work with visual display terminals (VDTs):
— Part 1: General introduction
— Part 2: Guidance on task requirements
— Part 3: Visual display requirements
— Part 4: Keyboard requirements
— Part 5: Workstation layout and postural requirements
— Part 6: Guidance on the work environment
— Part 7: Requirements for display with reflections
— Part 8: Requirements for displayed colours
— Part 9: Requirements for non-keyboard input devices
— Part 10: Dialogue principles
— Part 11: Guidance on usability
— Part 12: Presentation of information
— Part 13: User guidance
— Part 14: Menu dialogues
— Part 15: Command dialogues
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— Part 16: Direct-manipulation dialogues
— Part 17: Form filling dialogues
Annexes A and B of this part of ISO 9241 are for information only.
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Introduction
The keyboard is currently the principal input device used by operators to
enter information into interactive office computer systems. Keyboard
design can have a significant impact on efficiency, effectiveness and
satisfaction. The requirements and recommendations are based on
ergonomic principles.
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INTERNATIONAL STANDARD  ISO ISO 9241-4:1998(E)
Ergonomic requirements for office work with visual display
terminals (VDTs) —
Part 4:
Keyboard requirements
1 Scope
This part of ISO 9241 applies to linear detachable keyboards designed for stationary use. It provides
guidance on the design of keyboards used for typical office tasks so that the limitations and capabilities of
users are considered. It provides guidance based on ergonomic factors for keyboard layout arrangements,
the physical characteristics of the individual keys and the overall design of the housing containing the
keys. This part of ISO 9241 specifies methods for testing conformance by measuring the physical
attributes of a keyboard. It also includes a proposed alternative test method for keyboards that do not
conform to the physical design requirements and recommendations, based on a user performance test and
subjective rating scales.
2 Normative references
The following standards contain provisions which, through reference in this text, constitute provisions of
this part of ISO 9241. At the time of publication, the editions indicated were valid. All standards are
subject to revision, and parties to agreements based on this part of ISO 9241 are encouraged to investigate
the possibility of applying the most recent editions of the standards indicated below. Members of IEC and
ISO maintain registers of currently valid International Standards.
ISO 2469:1994, Paper, board and pulps — Measurement of diffuse reflectance factor.
ISO 7000:1989, Graphical symbols for use on equipment — Index and synopsis.
ISO 9241-3:1992, Ergonomic requirements for office work with visual display terminals (VDTs) —
Part 3: Visual display requirements.
1)
ISO 9241-5:— , Ergonomic requirements for office work with visual display terminals — Part 5:
Workstation layout and postural requirements.
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ISO/IEC 9995-1:1994, Information technology — Keyboard layouts for text and office systems — Part 1:
General principles governing keyboard layouts.
ISO/IEC 9995-2:1994, Information technology — Keyboard layouts for text and office systems — Part 2:
Alphanumeric section.
ISO/IEC 9995-4: 1994, Information technology — Keyboard layouts for text and office systems — Part 4:
Numeric section.
ISO/IEC 9995-5: 1994, Information technology — Keyboard layouts for text and office systems — Part 5:
Editing section.
ISO/IEC 9995-6: 1994, Information technology — Keyboard layouts for text and office systems — Part 6:
Function section.
ISO/IEC 9995-7: 1994, Information technology — Keyboard layouts for text and office systems — Part 7:
Symbols used to represent functions.
ISO/IEC 9995-8: 1994, Information technology — Keyboard layouts for text and office systems — Part 8:
Allocation of letters to the keys of a numeric keypad.
IEC 417:1973, Graphical symbols for use on equipment. Index, survey and compilation of single sheets.
3  Definitions
For the purposes of this part of ISO 9241, the following definitions apply.
3.1  Technical definitions
3.1.1
cursor
visual indication of the focus for alphanumeric input
1)
[ISO 9241-12:— ]
3.1.2
cursor keys
array of keys which control the movement of the cursor on the display screen and are labelled with arrows
indicating the direction of cursor movement caused by the individual keys
3.1.3
dished profile keyboard
keyboard in which the side profile of the keys resembles a continuous concave curve
(see figure 1)
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Figure 1 — Example of a dished profile keyboard
3.1.4
flat profile keyboard
keyboard that has a zero slope with the front at the same height as the back when placed on a flat work
surface
(see figure 2)
Figure 2 — Example of a flat profile keyboard
3.1.5
home row
row of the keyboard to which the fingers typically return between keystrokes
(see figure 3)
NOTE — On a typical keyboard, the home row is row C of ISO/IEC 9995 in the alphanumeric section as well as in
the numeric section.
Key
1  Home row
Figure 3 — Home row
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3.1.6
home row height
height from the centre of the strike surface of an unactuated key in the home row to the support surface
(see figure 4)
Key
1  Home row height
2  Row C
Figure 4 — Home row height
3.1.7
keyboard profile
geometric (i.e. flat, stepped, sloped, dished or sculptured) configuration of the top of the keys
3.1.8
keyboard slope
angle (a) between the plane of the key top surfaces (P-P) and the horizontal surface (H-H) as measured
across row A-E using the notation of ISO 9995-1
(see figure 5)
NOTE — For keyboards without an E row, use rows B to D.
Figure 5 — Keyboard slope
3.1.9
key displacement
key movement from its rest position to its fully depressed position
3.1.10
key force
force required to displace a key to a specified position
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3.1.11
key roll over
ability of a keyboard to register the correct order of activation of a set of keys
3.1.12
layout
spatial allocation of keys on a keyboard
3.1.13
numeric keypad
array of keys in the numeric section to which are allocated the ten digits 0 to 9 and the decimal separator
(see figure 6)
Figure 6 — Numeric keypad [1-2-3 (telephone) layout, left; 7-8-9 (calculator) layout, right]
3.1.14
palm-rest
platform placed in front of the keyboard or embedded in the keyboard on which the operator may place
the palm of their hands
3.1.15
principle section
alphanumeric, editing, function, and numeric sections
3.1.16
ramp action
kinaesthetic sensation during key actuation in which the force required to actuate the key increases as the
key is displaced
3.1.17
sculptured profile keyboard
keyboard in which the side view of the keytops is shaped in other than a straight line
3.1.18
sloped profile keyboard
keyboard in which the side profiles of the keys are all sloped (pitched) at the same angle with respect to
the base
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3.1.19
snap action
sudden drop in force required to further displace a key
3.1.20
stepped profile keyboard
keyboard in which the top of each key is parallel to the work surface but at a different height from the
work surface
(see figure 7)
Figure 7 — Example of a stepped profile keyboard
3.1.21
strike surface
area on the top surface of the key which the finger contacts during key actuation
3.1.22
tactile indicator keys
keys in the home row which contain a tactile aid for recentering the hands
3.1.23
visual display terminal (VDT)
functional unit consisting of at least a visual display and an input device
3.2  Usability-related definitions
3.2.1
diffuse reflection
diffusion by reflection in which, on the macroscopic scale, there is no regular reflection
[CIE Publ. 17.4:1987, IEV 845-04-47]
3.2.2
efficiency
resources expended in relation to the accuracy and completeness with which users achieve goals
[ISO 9241-11]
3.2.3
effectiveness
the accuracy and completeness with which users achieve specified goals
[ISO 9241-11]
3.2.4
feedback
information to the user indicating that a key has been actuated
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3.2.5
kinaesthetic feedback
sensation based on the cutaneous, joint, and muscle-spindle receptors of the hands, limbs and other body
parts
3.2.6
neutral hand/arm posture
hand/arm not deviated (bent or twisted) at a wrist, elbow or shoulder joint
3.2.7
reflectance
ratio of the reflected luminous flux to the incident flux under given conditions
[CIE Publ. 17.4:1987, IEV 845-04-58]
3.2.8
satisfaction
freedom from discomfort, and positive attitudes to the use of a product
3.2.9
specular reflection
reflection in accordance with the laws of geometrical optics, without diffusion
[CIE Publ. 17.4:1987, IEV 845-04-45]
3.2.10
usability
extent to which a product can be used by specified users to achieve specified goals with effectiveness,
efficiency and satisfaction in a specified context of use
[ISO 9241-11]
4  Guiding principles
The design of the keyboard can affect efficiency, effectiveness and satisfaction of a user. Design elements
interact such that optimizing one feature can degrade another. Trade-offs may be required to achieve an
acceptable balance. The objective of an ergonomic design is to ensure that the keyboard allows the user to
locate and operate the appropriate keys accurately, quickly and without discomfort. The keyboard
characteristics which influence keying performance include the layout arrangement of the alphabetic and
numeric keys, linguistic differences (national variants), the physical characteristics of the individual keys
and the overall design of the housing containing the keys.
The objective of an ergonomically designed system is to meet the needs of individuals while carrying out
specified tasks. To serve this purpose, different methods can be applied, for example, by selecting
appropriate tools which have been designed for general purpose use, by application of custom-designed
equipment for the specific task and for the specific users, or by providing adequate customization for the
components of tools and workstation. In addition, adequate training of the user can contribute
substantially to all objectives (efficiency, effectiveness and satisfaction).
Certain characteristics of the keyboard can influence the posture adopted by people working at a VDT
(see ISO 9241-5). For example, the height (thickness) of the keyboard combined with the height and
thickness of the work surface supporting it can result in users adopting poor postures.
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Efficiency, effectiveness and satisfaction of users depend on the selection of the keyboard design adequate
to the task of the user and on the use of other additional input devices. For example, provision of a
separate numeric pad can help the data input task.
When selecting design criteria for a keyboard for a specified task, the relevant considerations are based on
the functionality to be offered by the keyboard and by other input devices. These considerations can
suggest selecting the minimum possible size of the keyboard determined by the number and the adequate
grouping of the keys.
5  Performance criterion
The performance criterion is that the keyboard is usable for its designated purpose. It is considered usable
if users can achieve a satisfactory level of keying performance on a given task and maintain a satisfactory
level of effort and comfort. This objective can be met by adhering to the design requirements specified in
clause 6.
NOTE An alternative method for determining compliance is under development for keyboards that do not have
the design characteristics stated in this part of ISO 9241. One proposed test method is included in annex A.
6  Design requirements and recommendations
6.1  General design of the keyboard
6.1.1  Palm-rests
If the design includes a palm-rest then a depth of 50 mm to 100 mm should be provided in front of row A.
Where a palm-rest is not provided, the area in front of row A should be as near as possible to the front
edge of the keyboard.
6.1.2  Sections of the keyboard
The principal sections of a keyboard as defined in ISO/IEC 9995-1 shall be perceptually differentiated.
This can be accomplished by a spatial vertical and horizontal separation by at least half a key pitch or by
visual differentiation.
6.1.3  Home row height
The preferred home row height is not greater than 30 mm. However, the home row height of the keyboard
shall not exceed 35 mm. If an adjustment mechanism is provided, there shall be at least one adjustment
that allows it to comply with the height specification.
6.1.4  Slope of the keyboard
The recommended slope is 5° to 12° positive to the horizontal. The slope of the unadjusted keyboard shall
be between 0° and 15° positive.
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6.1.5  Profile of keyboard
The profile of the keyboard may be sloped, dished, stepped, sculptured or flat (see figures 1, 2 and 7).
6.1.6  Keyboard surfaces and material properties of keyboards
The visible surfaces of the keytops shall be matt finish.
The diffuse reflectance of the alphanumeric keytops should have values between 0,15 and 0,75 to
avoid undue luminance contrast to the equipment and other items within the field of view (see
1)
ISO 9241-5:— , 5.4.4).
The material of the surface with which the user comes into contact frequently should not have
unfavourable heat conductivity characteristics.
There should be no sharp edges or corners on the keyboard which could cause injury or discomfort to
users. The minimum radius at edges and corners on the keyboard housing should be 2 mm with a larger
radius at the corners.
6.1.7  Keyboard placement
The design of the keyboard shall permit it to be easily repositioned on the work surface, except for special
applications with clearly defined tasks. The keyboard shall be detachable. The keyboard should be stable
during use (i.e. it should not slip or rock) on a horizontal plane surface.
6.1.8  Keyboard slope adjustment mechanism
The keyboard slope should be adjustable. Any adjustment mechanism shall not compromise the
requirements for stability and placement. Adjustments shall not change unintentionally. Tools shall not be
required for adjustment purposes.
NOTE Support surfaces or other mechanisms designed for the purpose of placing or holding keyboards (e.g.
keyboard trays that provide x, y and z and slope adjustments are subject to design provisions given in ISO 9241-5.
6.2  Design of keys
6.2.1  Key layout and centre-line spacing
The layout of the keys shall conform to ISO/IEC 9995. The horizontal and vertical distances between two
adjacent keys in the alphanumeric and the numeric zones measured centre to centre shall be
19 mm – 1 mm. Outside the alphanumeric and numeric zones, other centre-line spacings are permitted,
but should not be smaller than 15 mm.
NOTE Certain keys can occupy more than one position in the grid and therefore the 19 mm centre to centre
restriction may not be applicable either vertically or horizontally or both (see ISO/IEC 9995-1).
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6.2.2  Keytop design
2
The strike surface of the keytops of alphanumeric keys shall be at least 110 mm in area, the width of the
strike surface shall be between 12 mm and 15 mm. The minimum strike surfaces apply to the keys in the
alphanumeric and numeric zones. Outside these sections, strike surfaces may be smaller, but not less than
2
64 mm .
NOTE  The appropriate dimensions of the keytop (keycap) depend on the key width, the key centre spacing, as
well as the strike surface and the key displacement.
Tactile indicators should be provided on the appropriate keys on the home rows of the alphanumeric
zones (i.e. position C04 and C07, ISO/IEC 9995-1) and numeric zones (i.e. C52, ISO/IEC 9995-1).
6.2.3  Key displacement and force
The key displacement shall be between 1,5 mm and 6,0 mm. The preferred key displacement should be
between 2,0 mm and 4,0 mm.
For displacement keyboards (see figure 8), the initial resistance (starting force or preload) shall be
between 25 % and 75 % of the force at the character generation point (for ramp action) or at the snap
point (for snap action). The force at the character generation point or at the snap point should be between
0,5 N and 0,8 N and shall be between 0,25 N and 1,5 N. The switch make action in the snap action shall
occur after the snap point but before the key force has returned to the snap point. The activation should
occur around the minimum force point after the snap point.
Figure 8 — Relationship between key displacement and key force
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The force/displacement characteristics across the alphanumeric keys should be consistent. The
force/displacement characteristics of a key should not depend on the part of the strike surface hit while
actuating.
6.2.4  Keying feedback
6.2.4.1  General
Actuation of a key shall be accompanied by feedback. Feedback can be kinaesthetic, auditory or some
combination of them. If the design allows only one method, then kinaesthetic feedback is preferred.
6.2.4.2  Kinaesthetic feedback
Ramp action displacement alone does not provide sufficient tactile feedback and should be accompanied
by auditory feedback (see 6.2.4.3).
6.2.4.3  Auditory feedback
Auditory feedback should be provided whenever tactile feedback is not provided. If the principal means is
auditory, the auditory signal shall be perceptible in the work environment. The auditory signal should be
an impulse sound (e.g. click of a relay switch) or tone (e.g. bell or beep sound). Supplementary auditory
feedback shall be suppressible (i.e. a volume control position that represents “off”). The feedback shall
occur within 100 ms after the key activation.
6.2.4.4  Visual feedback
Visual feedback should be used to indicate the long-term status of a particular key or keys (e.g. shift,
mode state). Such feedback should be clearly visible to the user. Visual feedback may be given by the key
itself or the keyboard, in which case it should be adjacent to or in close proximity to the key. In the case of
feedback appearing on the screen (for example in an operator information area) it should clearly indicate
which state the key or keys are in.
6.2.5  Rebound action (bounce)
In order to prevent unintended multiple event signalling from a single key actuation, the keyboard shall be
provided with either bounce-free switches or a means of ensuring that bounce will not cause unintended
activation.
6.2.6  Key roll-over
The keyboard shall correctly detect each key activation in correct order. This is achievable by adequate
key roll-over.
6.2.7  Key repeat function
Where a repeat function is provided, the fixed repeat rate shall be 10 to 20 activations per second after an
initial delay between 500 ms and 750 ms after the key is actuated. If the repeat function is activated by a
higher pressure force upon the key, the delay may be reduced.
NOTE  Initial delays of greater than 750 ms are likely to be perceived as too long.
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A user-adjustable repeat rate is preferred.
For certain irreversible functions (e.g. “erase” command) the repeat action facility should be suppressible.
6.2.8  Key legends
Key legends are used to indicate to the user which graphic characters or functions are allocated to the
keys. The legends consist of either graphical symbols representing the allocated graphic characters, text or
functions.
The provisions of this subclause only apply to Latin and Cyrillic based alphabets.
6.2.8.1  Graphical symbols
Graphical symbols, if used, shall be in accordance with ISO/IEC 9995 and with ISO 7000 and IEC 417
where applicable.
6.2.8.2  Geometric design of key legends
1)
All legends on keys shall be legible from the design reference posture (see ISO 9241-5:— , 3.6).
The height of primary legends on an alphanumeric key shall not be less than 2,6 mm. When a graphical
symbol, a full word or a well established abbreviation is used, the height shall not be less than 2,2 mm.
The width of the capital letters (except I and W) shall be between 50 % and 100 % of the height. The ratio
between the height and stroke width should be between 5:1 and 14:1.
For primary legends on all keys, the luminance contrast between luminance level of the background and
legends shall be a minimum of 3:1. Secondary legends should be perceptually different from the primary
legends on the same key. Legends should appear to have a sharp outline.
Dark characters on a light background are recommended.
6.2.8.3  Number and positioning of legends
The number of legends on any key should be kept to a minimum.
The positioning of the legends shall be in accordance with ISO/IEC 9995-1.
Where legends are too long for the keytop or where the function of the keys may change (e.g. emulation)
key legends can be provided on an overlay. Where legends are provided on overlays or the keyboard
housing, they should be adjacent to or in close proximity to the keys to which they refer. If space does not
allow for the implementation of this recommendation, a reference card should be provided. Overlays and
reference cards shall have a matt finish.
6.2.8.4  Durability of legends
The legends shall be legible throughout the intended life of the product. The legends shall be robust and
durable so that they are able to withstand normal wear and tear including regular cleaning.
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6.2.9  Cursor keys and keys in the editing section
Keys for the control of cursor movement shall be provided.
They shall be positioned as specified in ISO/IEC 9995-5.
Keys which activate erase or delete functions should be positioned in order to prevent inadvertent
activation.
6.2.10  Numeric keypad
The ten digits zero to nine shall be allocated to keys in the numeric zone ZNO in one of two ways, either
in the form of the 1-2-3 (telephone) layout or the 7-8-9 (calculator) layout. The telephone layout is
recommended. Layout and allocation of the numeric section is specified in ISO/IEC 9995-4.
6.2.11  Keytop shape
The keytops of normal size keys in the alphanumeric, cursor and numeric zones shall have either concave
or flat strike surfaces. The space bar may be flat or convex.
7  Measurement
7.1  General
The keyboard is measured on a flat horizontal surface.
According to ISO/IEC 9995-1, references to keyboard “row” are described by the codes “A”, “B”, “C”,
“D” and “E”.
“A” is the row closest to the user; “C” is the centre or “home” row.
7.2  General design of the keyboard
7.2.1  Palm-rests
Where a palm rest is provided, the depth is measured from the rear edge of the rest to the front.
7.2.2  Sections of the keyboard
If the principal sections of the keyboard are to be distinguished by spatial separation, the distance between
the closest edges of the bottom of the keys of the sections is measured.
If the principal sections of the keyboard are to be distinguished by other means than spatial separation, use
direct observation.
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7.2.3  Home row height
The home row height of the keyboard is measured from the centre of the keytop of the undepressed C row
to the supporting surface (see figure 9).
Key
1  Home row height
2  Row C
Figure 9 — Measuring the height of the keyboard at row C (home row)
7.2.4  Slope of the keyboard
The slope (a) is calculated from the difference in height between rows A and E (B and D in the case of
keyboards with no row E), measured at the top surface of the key (excluding convex keys), (see
figure 10).
If an E row is not provided, use rows B to D.
Figure 10 — Measuring the slope of the keyboard
7.2.5  Profile of keyboard rows
Use direct observation.
7.2.6  Keyboard surfaces and material properties of keyboards
Use direct observation for matt finish.
The diffuse reflection is the ratio of the diffuse reflected part of the reflected flux to the incident flux. Use
a reflectometer that has the geometric spectral and photometric characteristics described in ISO 2469. The
recommended test area is approximately 50 mm by 50 mm, therefore, it may be necessary to use a
representative sample of the top surface of the keyboard.
Measurement of thermal conductivity is not required.
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7.2.7  Keyboard placement
Determine whether the keyboard can be repositioned without the use of a tool. Verify that the keyboard is
detachable.
To determine keyboard slippage, use a suitable force gauge and push on the keyboard at the front corners
in the horizontal plane (see figure 11). Note the force required to initiate keyboard movement. Ensure that
the force applied is greater than 0,75 N and less than 13,0 N.
Measure on a horizontal smooth flat surface representative of an office worksurface.
Figure 11 — Measuring the force required to move the keyboard
To measure stability, measure the largest gap, if any, at one of the contact points between the keyboard
and the work surface. The gap should be less than 0,25 mm.
7.2.8  Keyboard slope adjustment mechanism
To determine stability and repositioning ease with the slope adjustment mechanism, measure placement
and stability using the metrics described in 7.2.8 with the slope adjustment mechanism in all positions.
Determine if the slope adjustment mechanism can be manually adjusted.
7.3  Design of keys
7.3.1  Key layout and centre-line spacing
Refer to ISO/IEC 9995 for assessment of key position.
Evaluate the horizontal and vertical distance between two adjacent keys by measuring the distance
between the centre of the keytops. Alternatively, the measurement can be done from edge to edge.
7.3.2  Keytop design
Evaluate the size of the strike surface by measuring the area of the top surface of the key from the width
and depth of the key (see figure 12).
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Figure 12 — Measuring ke
...