IEC 62646:2012

IEC 62646 ®
Edition 1.0 2012-09
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Nuclear power plants – Control rooms – Computer based procedures

Centrales nucléaires de puissance – Salles de commande – Procédures
informatisées
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IEC 62646 ®
Edition 1.0 2012-09
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Nuclear power plants – Control rooms – Computer based procedures

Centrales nucléaires de puissance – Salles de commande – Procédures

informatisées
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
CODE PRIX W
ICS 27.120.20 ISBN 978-2-83220-388-0

– 2 – 62646 © IEC:2012
CONTENTS
FOREWORD . 4
INTRODUCTION . 6
1 Scope . 8
1.1 Object . 8
1.2 CBP overview . 8
1.3 Exclusions from this standard . 9
1.4 Organisation of this standard . 9
2 Normative references . 10
3 Terms and definitions . 10
4 Abbreviations . 12
5 CBP policy requirements . 12
5.1 General . 12
5.2 Computerisation policy . 13
5.2.1 General . 13
5.2.2 Preliminary considerations . 13
5.2.3 Final decision on use of CBP . 14
5.3 Families of CBP . 15
5.4 Overview of computerisation features . 16
5.4.1 General . 16
5.4.2 Global requirements for computerisation . 16
5.4.3 CBP guidance. 16
5.4.4 Procedure based automation . 17
5.5 Output documentation . 18
6 Use of CBP . 18
6.1 General . 18
6.2 Environment of use . 18
6.2.1 General . 18
6.2.2 Use of CBP in computerised control rooms . 18
6.2.3 Use of CBP in a conventional or hybrid main control room . 18
6.2.4 Use of CBP in conjunction with paper based procedures . 19
6.2.5 Use of CBP outside the main control room . 19
6.3 Assistance to operators activities . 20
6.3.1 General . 20
6.3.2 Assistance to primary activities of the operator . 20
6.3.3 Assistance to secondary activities of the operator. 20
6.4 Operator coordination . 21
6.5 Output documentation . 21
7 CBP system . 21
7.1 General . 21
7.2 Safety requirements . 22
7.3 Integration of the CBP system into the HMI system . 22
7.4 CBP system independent from the HMI system . 22
7.4.1 General . 22
7.4.2 Non-safety requirements. 22
7.4.3 Connections between the CBP system and the HMI system . 23
7.4.4 Maintenance of the CBP system . 23

62646 © IEC:2012 – 3 –
7.5 CBP system failure . 23
7.6 Output documentation . 24
8 Detailed design requirements . 24
8.1 General . 24
8.2 Basic CBP features . 24
8.2.1 General . 24
8.2.2 Basic features necessary for CBP. 24
8.2.3 Presentation rules . 25
8.2.4 CBP display format layout . 25
8.2.5 Requirements for presentation of individual display elements . 26
8.3 Information given by CBP . 26
8.3.1 General . 26
8.3.2 Information for family 1 CBP . 26
8.3.3 Information for family 2 CBP . 26
8.3.4 Information for family 3 CBP . 27
8.4 Navigation . 27
8.4.1 General . 27
8.4.2 Navigation for family 1 CBP . 27
8.4.3 Navigation for family 2 and family 3 CBP . 28
8.5 CBP guidance . 28
8.5.1 General . 28
8.5.2 CBP access . 28
8.5.3 Diagnosis assistance . 28
8.5.4 Decision assistance . 29
8.5.5 Computerisation of CBP guidance . 29
8.6 Procedure based automation . 29
8.6.1 General . 29
8.6.2 Interactions between operators and procedure based automation . 30
8.6.3 Design of CBP to control the plant . 30
8.7 Other CBP facilities . 30
8.8 Output documentation . 31
9 CBP life cycle . 31
9.1 General . 31
9.2 Project organisation . 31
9.3 Project team . 32
9.4 Verification and validation programme . 32
9.5 CBP Programming . 32
9.6 Verification and validation of CBP . 33
9.6.1 General . 33
9.6.2 Technical verification of CBP . 33
9.6.3 Functional and ergonomic validation . 33
9.7 CBP deployment. 34
9.8 Output documentation . 35
9.9 CBP and CBP system maintenance . 35
9.10 Training of the operating staff . 35
Bibliography . 37

Table 1 – CBP Families . 15

– 4 – 62646 © IEC:2012
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
NUCLEAR POWER PLANTS –
CONTROL ROOMS –
COMPUTER BASED PROCEDURES
FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
this end and in addition to other activities, IEC publishes International Standards, Technical Specifications,
Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC
Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested
in the subject dealt with may participate in this preparatory work. International, governmental and non-
governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely
with the International Organization for Standardization (ISO) in accordance with conditions determined by
agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 62646 has been prepared by subcommittee 45A: Instrumentation
and control of nuclear facilities, of IEC technical committee 45: Nuclear instrumentation.
The text of this standard is based on the following documents:
FDIS Report on voting
45A/886/FDIS 45A/888/RVD
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.

62646 © IEC:2012 – 5 –
The committee has decided that the contents of this publication will remain unchanged until
the stability date indicated on the IEC web site under "http://webstore.iec.ch" in the data
related to the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct
understanding of its contents. Users should therefore print this document using a
colour printer.
– 6 – 62646 © IEC:2012
INTRODUCTION
a) Technical background, main issues and organisation of the Standard
This IEC standard focuses on computerisation of procedures used by the operating staff.
Procedures have always contributed to a large extent to NPP safety and availability and,
now, the use of computer technology to provide enhanced guidance to the plant operators
is increasing and becoming current practice. This standard also provides guidance for the
decision on the extent the procedures should be computerised.
It is intended that the Standard be used by nuclear power plant designers, utilities
operating staff, systems evaluators and by regulatory engineers.
b) Situation of the current Standard in the structure of the IEC SC 45A standard series
IEC 62646 is the third level IEC SC 45A document tackling the generic issue of
computerised procedures.
IEC 62646 is to be read in association with IEC 60964 and with IEC 61839. IEC 60964 is
the appropriate IEC SC 45A document providing guidance on operator controls,
verification and validation of design, application of visual display units in the control room,
whereas IEC 61839 establishes functional analysis and assignment guidance for allocating
functions between operators and systems.
For more details on the structure of the IEC SC 45A standard series, see the item d) of
this introduction.
c) Recommendations and limitations regarding the application of the Standard
It is important to note that this Standard establishes no additional functional requirements
for safety systems.
This standard deals with technical requirements and Human Factor Engineering related to
Computer Based Procedures (CBP). However it does not provide detailed guidance on
ergonomic design of control centres as it is treated in the ISO 11064 series of standards,
nor on task allocation between human and systems dealt with in IEC 61839 and on cyber
security, which is developed in IEC 62645. It also excludes the organisation for
maintenance of procedures.
Aspects for which requirements and recommendations have been provided in this
Standard are:
– the establishment of a policy for computerisation of procedures, especially which types
of procedure should be computerised and to what extent. The different families of CBP
(Computer Based Procedures) to be aimed at, with their associated features, are then
defined. Finally, the safety aspects of CBP are considered;
– the use of CBP inside and outside of the MCR (Main Control Room), in possible
conjunction with paper based procedures, as well as the assistance provided to
operator activities, including user coordination;
– safety and non safety design requirements for the digital system processing CBP, and
considerations about what to do in case of failure of this system;
– detailed requirements and recommendations related to the functional features of CBP,
from the basic ones to the most sophisticated ones, i.e. information, navigation,
guidance and plant control;
– the CBP life cycle, from the set-up of the project to the CBP maintenance and the
operator training via design and implementation.
To ensure that the standard will continue to be relevant in future years, the emphasis has
been placed on issues of principle, rather than on specific technologies.
d) Description of the structure of the IEC SC 45A standard series and relationships
with other IEC documents and other bodies documents (IAEA, ISO)
The top-level document of the IEC SC 45A standard series is IEC 61513. It provides
general requirements for I&C systems and equipment that are used to perform functions
important to safety in NPPs. IEC 61513 structures the IEC SC 45A standard series.

62646 © IEC:2012 – 7 –
IEC 61513 refers directly to other IEC SC 45A standards for general topics related to
categorization of functions and classification of systems, qualification, separation of
systems, defence against common cause failure, software aspects of computer-based
systems, hardware aspects of computer-based systems, and control room design. The
standards referenced directly at this second level should be considered together with
IEC 61513 as a consistent document set.
At a third level, IEC SC 45A standards not directly referenced by IEC 61513 are standards
related to specific equipment, technical methods, or specific activities. Usually these
documents, which make reference to second-level documents for general topics, can be
used on their own.
A fourth level extending the IEC SC 45A standard series, corresponds to the Technical
Reports which are not normative.
IEC 61513 has adopted a presentation format similar to the basic safety publication
IEC 61508 with an overall safety life-cycle framework and a system life-cycle framework.
Regarding nuclear safety, it provides the interpretation of the general requirements of
IEC 61508-1, IEC 61508-2 and IEC 61508-4, for the nuclear application sector, regarding
nuclear safety. In this framework IEC 60880 and IEC 62138 correspond to IEC 61508-3 for
the nuclear application sector. IEC 61513 refers to ISO as well as to IAEA GS-R-3 and
IAEA GS-G-3.1 for topics related to quality assurance (QA).
The IEC SC 45A standards series consistently implements and details the principles and
basic safety aspects provided in the IAEA code on the safety of NPPs and in the IAEA
safety series, in particular the Requirements NS-R-1, establishing safety requirements
related to the design of Nuclear Power Plants, and the Safety Guide NS-G-1.3 dealing with
instrumentation and control systems important to safety in Nuclear Power Plants. The
terminology and definitions used by SC 45A standards are consistent with those used by
the IAEA.
NOTE It is assumed that for the design of I&C systems in NPPs that implement conventional safety functions
(e.g. to address worker safety, asset protection, chemical hazards, process energy hazards) international or
national standards would be applied, that are based on the requirements of a standard such as IEC 61508.

– 8 – 62646 © IEC:2012
NUCLEAR POWER PLANTS –
CONTROL ROOMS –
COMPUTER BASED PROCEDURES
1 Scope
1.1 Object
This International Standard establishes requirements for the whole life cycle of operating
procedures that the designer wishes to computerise. It also provides guidance for making
decisions about which types of procedures are to be computerised and to what extent. Once
computerised, procedures are designated as "Computer Based Procedures" (CBP).
Enhancing safety, easing operation and increasing NPP availability have always been greatly
valued aims which, during NPP operation, rely to a large extent on the operating staff and on
operating procedures. Digital technology is currently contributing by providing efficient help to
do this at the automation level.
In addition, the use of computer technology to provide formats of operating procedures to the
plant operators , on-line and in real time, is increasing and becoming current practice. This
can be done both for normal operating situations and also as advisory formats for use in
abnormal situations. When properly implemented and kept up-to-date, such operating
procedures can provide enhanced support for greater safety and operator effectiveness
compared to paper based procedures. Their preparation demands great care and close
interaction with operators and plant designers, and will also need close co-operation with I&C
designers.
CBP have many common points with paper based procedures. This standard focuses only on
what is specific to CBP.
1.2 CBP overview
Procedures provide the operators with two types of high level elements:
• information, i.e. explanations or data displayed in order to enable the operator to control
the process, assess the plant situation, understand operating strategies and make
appropriate decisions,
• guidance, i.e. a set of ordered steps for prompting and helping the operator to operate the
process and the plant equipment.
Information and guidance are combined to minimise operators errors and to optimise
efficiency of plant operation.
These elements can be of a varying level of detail depending on the procedure policy, which
aims to benefit from operator experience and predefined guidelines.
Computerisation of procedures can provide, according to the specified design policy:
• enhanced process and plant equipment information,
• enhanced operator guidance,
___________
Operators may be male or female, so that in this standard, “he” is a shortcut for “he / she” and “his” is a
shortcut for “his / her”.
62646 © IEC:2012 – 9 –
• optional automatic plant control.
However, introducing such procedures requires attention to the following issues:
• defining a clear policy on the scope of procedures, level of guidance and possible direct
process control for example, taking into account experience from plant operation and
human capabilities as well as organisational and technological issues,
• designing a safe and reliable CBP system, and also providing an appropriate back-up
including operating procedures covering the assumed failure of the CBP system,
• validating a combination of plant operation strategies, formats presentation and human
capabilities, as well as digital issues,
• maintaining the operator in the loop, i.e. ensuring adequate priority of human action
versus computerised actions and preventing the loss of knowledge.
1.3 Exclusions from this standard
In order to design CBP efficiently and properly, some important inputs should have already
been decided and are therefore outside the scope of this standard:
• functional analysis and assignment
IEC 61839 specifies functional analysis and assignment procedures and gives rules for
developing criteria for the assignment of functions either to operators or to systems,
• human factors design guidelines.
ISO 11064 series of standards provides guidance on human-centered design activities
throughout the life cycle of a computer-based interactive system.
In addition, IEC 60964 and IEC 60965, which provide requirements and recommendations for
the main control room and supplementary control point arrangements, apply to the
implementation of CBP in new nuclear power plants. Complementary advice for implementing
CBP in case of main control room retrofitting is given in 6.2.3 of this standard.
This standard also excludes:
• computer security, which is necessary to protect the whole life cycle of CBP, but is not
restricted to computerisation of procedures. Nevertheless, this topic is to be considered
when computerising operating means. IEC 62645 deals with cyber-security,
• requirements on the implementation for CBP functions of software and hardware of
computer systems for CBP has to be implemented in line with its safety class in
compliance with IEC 61513,
• the organisation for maintenance of procedures.
1.4 Organisation of this standard
Clause 2 lists the reference documents.
Clause 3 gives definitions relevant to this standard.
Clause 4 lists the abbreviations used in this standard.
Clause 5 provides an overview of CBP. It presents recommendations for the development of a
policy for computerisation of procedures, based on the type of procedure to be implemented.
Three generic types (termed “families”) are proposed, for which general and specific guidance
is provided. Guidance related to the safety requirements of CBP systems is also provided.
Clause 6 gives requirements for use in different environments, inside and outside of the MCR
(Main Control Room) and possibly in conjunction with paper based procedures. It then
considers assistance to and coordination of operator activities.

– 10 – 62646 © IEC:2012
Clause 7 deals with the digital system which processes CBP. It first considers safety and non-
safety requirements, then gives requirements for handling failures of this system.
Clause 8 focuses on the detailed requirements and recommendations related to the functional
features of CBP, from the basic ones to the most sophisticated ones, i.e. information,
navigation, guidance and plant control. Miscellaneous options that could ease CBP use are
also given.
Clause 9 considers the CBP life cycle, from the set-up of the project to the CBP maintenance
and the operator training via design and implementation.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and
are indispensable for its application. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any
amendments) applies.
IEC 60671, Nuclear power plants – Instrumentation and control systems important to safety –
Surveillance testing
IEC 60880, Nuclear power plants – Instrumentation and control systems important to safety –
Software aspects for computer-based systems performing category A functions
IEC 60964:2009, Nuclear power plants – Control rooms – Design
IEC 60965:2009, Nuclear power plants – Control rooms – Supplementary control points for
reactor shutdown without access to the main control room
IEC 61513, Nuclear power plants – Instrumentation and control important to safety – General
requirements for systems
IEC 61772, Nuclear power plants – Control rooms – Application of visual display units (VDUs)
IEC 61839, Nuclear power plants – Design of control rooms – Functional analysis and
assignment
IEC 62138, Nuclear power plants – Instrumentation and control important for safety –
Software aspects for computer-based systems performing category B or C functions
IEC 62241:2004, Nuclear power plants – Main control room – Alarm functions and
presentation
ISO 11064 (all parts), Ergonomic design of control centres
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
back-up system
alternative equipment for plant monitoring and control designed to be used in case of failure
of the normally used HMI system

62646 © IEC:2012 – 11 –
3.2
Computer Based Procedures
CBP
interactive computer-application used to present procedural guidance to plant operators and
which may additionally contain dynamic process information including access to operator
controls
Note 1 to entry: Unlike paper based procedures which are static documents, CBP offer dynamic reading options.
These options allow the operator to "navigate" from one step to others in different enhanced ways, to place
bookmarks, and to use parallel displays.
3.3
CBP system
digital system implementing the CBP
Note 1 to entry: CBP may be implanted in the HMI system, together with other plant control functions, or may be
implemented in a standalone CBP computer.
3.4
format
display format
pictorial display of information on a visual display unit (VDU) such as message text, digital
presentation, symbols, mimics, bar-charts, trend graphs, pointers, multi-angular presentation
[SOURCE: IEC 60964:2009, 3.7]
3.5
high-level mental processing
human act to process and/or interpret information to obtain reduced abstract information
[SOURCE: IEC 60964:2009, 3.12]
3.6
Human Machine Interface
HMI
the interfaces between operating staff and I&C system and computer systems linked with
plant. The interface includes displays, controls, and the operator support system interface.
[SOURCE: IEC 60964:2009, 3.13]
3.7
navigation
a function, which supports the operators in locating the position of desired information in a
VDU-based information system, and also in guiding the selection of displays
[SOURCE: IEC 62241:2004, 3.29]
3.8
Operating Procedures
OP
a set of documents specifying operational tasks it is necessary to perform to achieve
functional goals
[SOURCE: IEC 60964:2009, 3.19]
3.9
paper based procedures
OP (see 3.8) that are printed on paper sheets

– 12 – 62646 © IEC:2012
3.10
Postulated Initiating Event
PIE
an event identified during design as capable of leading to anticipated operational occurrences
or accident conditions
[SOURCE: IAEA Safety glossary, 2007]
3.11
sequence
procedure sequence
a set of elementary steps in a procedure that is to be completely executed in order to reach a
functional objective
Note 1 to entry: A partial execution of a sequence could either lead to malfunction or failure of circuits or
equipment or jeopardise the execution of a function.
Note 2 to entry: Generally, a procedure encompasses several sequences to achieve its global functional
objective.
Note 3 to entry: A sequence may consist of a single step.
3.12
Supplementary Control Point
SCP
a location from which limited plant control and/or monitoring can be carried out to accomplish
the safety functions identified by the safety analysis as required in the event of a loss of
ability to perform those functions from the main control room. The supplementary control point
may be a special control room, but in many cases comprises a set of control panels and
displays in switchgear rooms or similar areas
[SOURCE: IEC 60965:2009, 3.5]
3.13
Visual Display Unit
VDU
type of display incorporating a screen for presenting computer-driven images
[SOURCE: IEC 60964:2009, 3.31]
4 Abbreviations
CBP Computer Based Procedures
HMI Human Machine Interface
HVAC Heating, Ventilation, and Air Conditioning
MCR Main Control Room
OP Operating Procedures
PIE Postulated Initiating Event
SCP Supplementary Control Point
VDU Visual Display Unit
5 CBP policy requirements
5.1 General
This clause provides an overview of CBP. It presents recommendations for the development
of a policy for computerisation of procedures, based on the type of procedure to be
implemented. Three generic types (termed “families”) are proposed, for which general and

62646 © IEC:2012 – 13 –
specific guidance is provided. Guidance related to the safety requirements of CBP systems is
also provided.
5.2 Computerisation policy
5.2.1 General
This activity shall be embedded in the framework of specifying the control room concept, the
overall I&C architecture, the definition of human factors policy and the utility operating
principles (see IEC 60964:2009, Clause 5).
It should be supported by feedback of experience analysis, conceptual studies, possibly some
prototyping, performed either as an input to the design or as an early step of the design.
The designer shall decide the types of procedures subject to computerisation and the extent
of this computerisation.
The reasons for computerisation of procedures shall be stated in the governing project plan,
as they will strongly influence which procedures will be computerised and to what extent.
Implementing CBP will not necessarily resolve operating strategy or staffing problems, but a
design study for a CBP may help to clarify the nature of those problems and help to identify
ways for problem resolution at an early stage.
NOTE Possible consequences on operating staff organisation, main control room layout, operating strategies,
procedure scope, automation level, etc. are out of the scope of this standard.
Types of procedures that may be computerised are:
• procedures guiding normal plant operation in normal conditions, for example plant
start-up, or procedures guiding elementary tasks, pipework warm-through, or load
reduction and return to power,
• accident procedures, beyond design basis procedures,
• alarm response procedures,
• fire handling procedures,
• loss of electrical power procedures, and any types of procedures dedicated to unusual
conditions,
• technical specification procedures,
• periodic tests procedures designed according to IEC 60671, for example dedicated to flux
calibration or to reactor trip, or any other periodic tests procedures,
• technical component sheets, offering easy access to specific device data on the screen-
based HMI.
5.2.2 Preliminary considerations
In addition to functional analysis and assignment and human factors design guidance which
are excluded from the scope of this standard by 1.3, some other basic topics shall be
considered at an early stage of the design. These are:
• national regulatory issues,
• operating strategies
this is a functional issue independent from computerisation, for example a decision has to
be made between state based and event based strategies in the event of an accident,
• operating staff organisation
when constructing a new plant or modernising an existing plant, CBP design may be made
an integral part of the overall control room design or redesign, which makes it necessary
to apply accepted human factors engineering methods,

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• operating staff experience feed-back
what is good, what should be improved, what is missing in any existing CBP or paper
based solution should be identified;
in addition, the designer may consider that only the operating strategy, or on the contrary,
only the detailed part of the procedures, should be computerised,
• the operator training policy,
• data issued from the plant instrumentation,
NOTE The CBP guidance level depends on available instrumentation.
• integration of the CBP processing into an HMI system, if digital, or use of a dedicated
system to process CBP connected or not connected to a digital HMI system.
A preliminary CBP policy and the types of procedures that could be computerised should be
defined from these considerations.
5.2.3 Final decision on use of CBP
To make a final decision on the types of procedures to be computerised, the following issues
should be considered in the conceptual design:
• identification of the types of procedures that could be processed simultaneously in normal
operation, in case of fire, in case of a loss of electrical power supply, in case of a Periodic
Test, in case of a PIE,
• assessment of the amount of VDU necessary for these procedures,
• assessment of the maximum number of procedures that could be processed in parallel by
a single operator or by the entire operating staff to operate in the case of an occurrence of
the worst design basis combination of events,
• assessment of the maximum number of windows that could be displayed in parallel in the
worst cases on a single workstation or on all room workstations,
• allocation of operating staff's tasks in a complementary way to CBP and paper based
procedures.
The above assessment should be made considering the control room concept. Items to be
looked at are:
• the set of work stations and work places where CBP are intended to be used, in the main
control room and at all other control points,
• the fact that a procedure could be temporarily abandoned without being terminated, for
example in case of an alarm outbreak,
• the maximum amount of information to be displayed in a format,
• the performance of the CBP system, in particular regarding displays, memory capacities,
navigation,
• adequate additional margins in order to ease future modifications.
These considerations may challenge aspects of the CBP impl
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