the development of a touch screen based communications terminal

ELSEVIER International Journal of Industrial Ergonomics 18 (1996) l - 13

Industrial Ergonomics

The development of a touch screen based communications terminal

Bruce Thomas *, Ian McClelland Philips Corporate Design, Postbu.s 218, NL-5600 MD Eindhot,en, The Netherlands

Received 30 April 1994: revised 25 March 1995

Abstract

This paper discusses a successful attempt to improve the design of a communications terminal lbr professional applications involving significant improvements to customer and operator contact, and improving the level of operator focus during the design phase. This included visits to sites to capture requirements through interview and observation of working practices, and to get insight into typical communication tasks. A clear task focus was maintained during the design phase by using a dialogue description tool, the Task Action Description, developed in-house to support the integration of the dialogue specification, the graphic design and the software design. Customer and operator feedback on the design was obtained. The value of team work is also discussed. The success of the design can be attributed to a direct involvement of users in the development process and to the integration of human factors specialists, graphic designers, software engineers and marketing experts in the development team. The conclusions drawn highlight: (1) the importance of direct first hand exposure to the daily working environment of the operators by the team as a whole: (2) the problem of how to articulate operator requirements in such a form that they are taken into account in the design development; and (3) the progressive evolution of organisations and changes in work practices.

Relevance to industry

The paper presents an industrial case study illustrating the value of a process with user involvement from the early stages, the relationships between different professionals in an industrial setting and the nature of organisational changes which could facilitate the involvement of human factors in industry.

Kexwords: Touch screen; Communication; User involvement: Interaction specification; Work practice; Organization

1. Introduct ion

* Corresponding author. i This paper is an expanded version of a paper with the same

title given at the 38th Annual Meeting of the Human Factors and Ergonomics Society (Thomas and McClelland, 1994).

This paper discusses the successful deve lopment o f a communica t ions terminal (the DS 3000) for

professional applicat ions (police, fire, ambulance ,

traffic services, etc.) invo lv ing s ignif icant improve-

ments to cus tomer and operator contact, and improv-

0169-8141/96/$15.00 {:3 1996 Elsevier Science B.V. All rights reserved SSD111169-8141(95)00025-9

2 B. Thomas, L McClelland/hlternationalJournalofhtdustrialErgonomics 18(1996) 1 13

ing the level of operator focus during the design phase.

Prior to this project most designs were based primarily on commercial and technical specifications. These specifications were written by specialists with, in some cases, detailed knowledge of the particular requirements of customers built up over many years. Often contacts within customer organisations were also handled through internal communications specialists who represented the interests of the operators (the end users).

In this project we wanted to achieve more direct involvement of customers and operators in identify- ing operator requirements and evaluating design proposals than hitherto. However 'conventional wis- dom' limited the opportunities made available to undertake comprehensive task analysis work, work flow observations, environmental assessments, and similar activities often carried out by ergonomists. We had to take a very pragmatic view on how we could contribute to the design of the terminal. Conse- quently the main emphasis of the ergonomics contribution was in the design phase. A higher level of operator focus than previously was the case was maintained in this phase by developing dialogue documentation methods which were explicitly task based.

2. The Philips DS 3000 terminal

The DS 3000 is the most recent in a long line of Philips communication system terminals used to control communication activities such as found in police forces, fire brigades, ambulance services and other private communications operators. In this paper, the focus is on UK police applications.

The DS 3000 is a touch screen based terminal designed to handle a complex combination of radio and telephone communications, intercoms, alarms, and a number of ancillary functions. The predecessor was the DS 2000, the first such communications terminal to make use of touch screen technology. A major goal for the DS 3000 development team was to improve on the DS 2000 in terms of the functional capability of the system, the interaction design and the graphic design, and thereby maintain Philips competitive position in this market.

The new system had to adhere to a mandatory British government specification written under con- tract by Smith Associates Ltd. (Graham-Rack et al., 1988). This specification demanded that many new functions had to be available which were not incor- porated in previous systems. The specification did not indicate levels of priority for the new functionality from the operators' point of view, nor was there readily accessible information concerning how the new functions might be used in practice.

The programme of work undertaken in the design of the DS 3000 is described in the following sec- tions.

3. Literature study

A first step of the design work was to consult the human factors literature concerning the use of touch screens. This provided some essential insights for the design of the individual elements on the screen (hot spots or buttons), as well as some of the limitations and advantages of the technology. Particularly valuable was the Greenstein and Arnaut (1988) review. Greenstein and Arnaut conclude that the advantages of touch screens are that they make use of direct eye-hand co-ordination, they have a direct input- output relationship, all valid inputs are displayed and training is minimized. The disadvantages of touch screens are that the user must sit within arm's length of the display, they can cause arm fatigue, the arm and finger often block the line of sight to the screen and target resolution is limited due to the size of operators' fingers.

The following principles for the design of the DS 3000 were derived from the literature: 1. The system should respond to the last key touched

rather than the last touch itself, that is the last valid key touch before finger exit is accepted. Beaton and Weiman (1984) argue that this pro- vides better responses. They also suggest that when representing keys on touch screens, key height affects error rate more than key width.

2. Buttons should have a greater separation than is required for hard keys. Benel and Stanton (1987) found that accepted minimum values for hard keys were too small for touch technologies. Large distances between keys, however, produce slower

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times. For technologies using scanning beams the finger must be removed from the scanning area be(bre going to the next contact point, thus slow- ing down operation.

3. For numeric entry, use compressed keypads with square keys. Martin (1988) looked specifically at the problem of implementing keypads on touch screens and found that this yielded the best per- tbrmance. She suggested that square keys permit a level of automaticity to develop in motoric behaviour, since the centre to centre key spacing is constant. With respect to the choice of touch screen tech-

nology, infra-red and surface acoustic wave (SAW) screens were proposed for the DS 3000. Neither appeared to have a clear advantage. Baggen (1987) compared 6 touch screen devices over a variety of task and environmental conditions. He found that overall the infra-red gave the best performance. In- fra-red screens are, however, limited by the number of possible beams, and may have as few as 25 × 40 touch points (Logan, 1985). Acoustic screens are somewhat better in this respect. Even if high resolution is not needed, it is desirable because it allows touch points to be averaged to better identify the intended target. In the case of the DS 3000, the

purchaser is offered a choice of either infra--red or SAW screens.

4. Contextual studies

A critical part of the work programme was to embark, at an early stage, on a series of site visits. The purpose of these visits was to obtain an understanding of the users and the tasks they were performing, as well as the physical environment in which the communications terminals would be located.

In total, 6 police control rooms were visited. The communications terminals used were in 5 cases the DS 2000, and in the remaining case a traditional 'key and lamp' (i.e., not screen based) system was used. The DS 2000 is illustrated in Fig. 1. Semi- structured interviews were carried out with supervi- sory staff and operators. Table I shows the numbers and function of the interviewees. Operators were also observed at work. Through these observations and interviews a detailed understanding was built up of the work carried out, and the particular tasks associ- ated with using the terminals. The interviews provided valuable insights into the way in which the DS

Fi~. 1. The DS 2000.

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Table l Control room personnel interviewed in the course of the study

Police force 1 2 3 4 5 6

Operators interviewed 10 10 8 10 2 6 Supervisors interviewed 2 2 2 2 1 1 Managers interviewed 2 1 I 1 1 1

3000 terminal could be tailored to support the operators more effectively in their work.

All the members of the design team (ergonomist, designer, software engineer, mechanical engineer and product manager) visited the control rooms. This greatly facilitated subsequent design team discussions during the development when operator issues arose. The understanding of the tasks the users were actually performing, built up during the visits, went a long way to ensuring that the system was developed to support users, rather than simply supplying sophis- ticated functionality.

Some of the main findings from the context of use studies are summarised below.

4.1. S ta f f ing

The communications were handled by male and female operators, who were police officers or

'c ivi l ians ' . The control room supervisor was usually a police officer. All operators were trained in communications procedures and had a thorough knowledge of the tasks. The operators rotated jobs on a shift basis and provided back-up to colleagues in times of high stress. Each communications terminal was occupied by different people at different times. not only on different shifts, but sometimes also during a shift as workloads and tasks were changed.

4.2. P h y s i c a l con tex t

Control rooms can vary in size from small one or two person operation, for example controlling communications for an island police force, to large scale control rooms with over 30 operators controlling communications for a whole British county.

In all of the control rooms visited, entry was very restricted. Permission to enter was only given from within the control room itself. The specification for the DS 3000 foresaw the possibility of controlling this entry and exit, as well as local surveillance equipment, via the communications terminal.

A variety of equipment is located on the desks in such control rooms. Light levels are often subdued during the daytime and dark at night time to reduce

Fig. 2. Control room with 'traditional' communications panel.

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Fig. 3. A typical control room.

disturbing reflections and improve the contrast bal- ance between different surfaces in the operators work area. The screen design for the DS 3000 therefore had to take into account its use in low lighting conditions and the possibil i ty of light sources caus- ing problems with reflections.

The communications terminals are often placed alongside terminals for the police national computer. Many communications deal with enquiries from officers in the field to this computer. Further calls are logged in note-books and logs, and operators also jot down on pieces of paper the content of information

Fig. 4. Control room for a small police force.

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they are given or wish to convey. As well as the main communications terminal, additional telephones and intercoms provide further communications channels, as well as a back-up in case of failure of the main system.

Illustrations of control rooms are shown in Figs. 2-4.

4.3. Work patterns

Police communication control rooms are typically in operation 24 hours a day. They support all types of communications from routine needs to 'major incidents'. Consequently, the work load can fluctuate dramatically and unexpectedly between periods of almost complete inactivity to periods of high demand. At any time, operators may be required rapidly to switch between a variety of telephone links and radio channels. When demand is high, the need for rapid and precise response may literally be a matter of life or death. So considerable demands are placed on the user interface design in terms of the ease with which system state can be understood, and actions can be executed.

An operator working with radio channels moni- tors and controls the radio communications of police officers working in the field. The operator must respond to these officers. The officers may request assistance or information, or may simply provide an activity status report. The communication is heavily dependent on a good working relationship between police officers and control room operators, and in particular the officers in the field must have confi- dence in the reliability of the control room staff.

Various telephone lines provide vital links in the communications network not covered by the mobile radio system. These links are to the general public, which includes responding to emergency calls (the '999' number in the UK), and sometimes to more general police lines. Other lines exist to the other emergency services (fire and ambulance), other police forces and other organisations. In many cases, telephone calls trigger actions to be taken by officers in the field, and the relevant information is commu- nicated by radio. In some circumstances telephone lines can be directly linked to radio channels.

In most control rooms, apart from those with only one or two man operation, responsibility for commu-

nications is divided between operators working on parallel terminals. Police control centre manage- ments vary considerably in their approach to the allocation of tasks and the way tasks are shared between operators. In some control rooms, there is a division between operators controlling telephones and operators controlling radio channels. In other control rooms, operators control both radio and telephone communication, but do so on the basis of a particular geographical area. In some places, particular operators perform special duties, for example controlling motorway (freeways in the US) roadside breakdown telephones.

5. Keypad study

One issue raised in the field studies required a more traditional 'experimental' approach. At 5 of the sites, numeric keypads were represented on touch screens. Control room operators complained that, when these keypads were used for dialling telephone numbers, they were slow and error prone. At one other site, hard keypads had been installed following similar complaints. Improved operator performance was reported as a result. For the DS 3000 it was thought that technical advances in touch screen technology could have eliminated these problems or, aI least, reduced them. Further, equipping each terminal with a hard keypad would require additional expense which needed to be justified.

A major distinction between use of a keypad and use of other control elements is that the keying actions using the keypad occur in sequences rather than being isolated events. Dialling telephone numbers, for example, can typically involve a sequence of 10 digits. Sears (1991) examined the use of a touch screen for sequential entry compared to more conventional means. Sears compared performance on a touch screen alphanumeric keyboard with a mouse activated keyboard and a standard QWERTY keyboard for typing strings of 6, 19 and 44 characters. Higher typing speeds were achieved with the QW- ERTY keyboard.

Beringer (1989) compared several types of mechanical keypad with two types of touch input device in a menu selection task. He found that there was "no practical degradation in performance when sub-

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Table 2 Mean scores for the performance of each of the 3 input media

Measure Keypad type

Hard Surface Infra-red acoustic wave

Strings dialled in 10 min 121.75 112.08 116.50 Incorrect strings (raw) 10.08 11.50 15.17 Incorrect strings 8.12% 10.23% 12.67% (proportional) Correct strings 111.67 100.58 101.33

stituting the touch input devices for bezel-mounted hardware keys". He did not, however, address the issue of keying sequences of digits.

A small experiment was carried out to determine whether the hard keypad was sufficiently superior compared to surface acoustic wave or infra-red touch screen technologies to warrant the necessary invest- ment in providing it. Subjects were asked to dial as many 'telephone' numbers as they could within 10 min using each of the input media. Measures taken were personal preference, number of dialled strings, number of incorrect strings (raw and adjusted scores), and number of correct strings.

Eleven of the 12 subjects rated the hard keypad as being superior. No clear preference between the two touch screen keypads emerged on the basis of personal preference. A summary of the results of the objective measures is shown in Table 2. These results confirmed our hypothesis that the hard keypad performed better than keypads on a surface acoustic wave or an infra-red touch screen for entering number sequences. The surface acoustic wave keypad performed better than the infra-red keypad.

6. The design

The information collected from the interviews and observations during the visits helped the team clearly to identify the main areas of difficulty and propose improvement targets for the design work. It also enabled a task hierarchy to be synthesised as the basis for the dialogue designs for the DS 3000.

A number of design goals were formulated: 1. Enable rapid access to all parts of the system.

2, Provide immediate access to high priority items (communications channels) at all times. Tile observations and interviews revealed the absolute priority of incoming calls, and the need for immediate access to all communications channels.

3. Ensure that the operators understand how to oper- ate all parts of the system, including those they may not previously have encountered. In unfamil- iar emergency situations, such as in an 'incident' configuration, the operator must still respond promptly and accurately.

4. Create a visual environment which is comfortable to use for extended periods - 8 h shifts or even longer.

5. Allocate functions according to operational procedures and organise the system according to operational hierarchies.

6. Ensure that operators and supervisors are able to determine the state of the system at all times, just by looking at the screen. In order to achieve the above goals, the following

graphics and interaction principles were used to guide the design: 1. Give first priority to incoming calls and provide

access to communications at all times. 2. Avoid high impact colours. The DS 3000 user

will be working with the touch screen for most of an 8 h work shift. The graphics designers chose a colour scheme based on soft, pastel colours to create a restful effect on operators.

3. Place items used most frequently in the lower half of the screen to avoid fatigue when reaching for them.

4. Provide immediate feedback for all operator actions. Visual feedback is given every time an item is activated - a short flash or a change of colour. Audible feedback, a 'click' sound, is synchro- nised with the visual feedback to reinforce the illusion that a 'button' has been activated. The 'click' was deliberately set low to avoid acoustic disturbance, but just loud enough to provide the operator with confirmation.

5. Use simple interactions. Effective use of the system is supported through use of a simple interaction paradigm: touch to activate, touch again to deactivate or change state.

6. Create a 'flat ' system structure. Efficient use of the system is supported through minimum naviga-

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tion. All functions accessible to operators can be reached within 4 levels. All functions required on a daily basis can be reached within two levels.

7. Maintain a consistent interaction style. A consistent style was developed for opening, closing and interacting with dialogue boxes and their con- tents.

8. Make sure that the operator always has an overview of where he is in the system. The layout of buttons and dialogue boxes ensured that the path to a particular part of the system was always visible, and selected functions along the path were highlighted. The possibility to have multiple dialogue boxes open at one time was strictly limited. This ensured that the screen did not become cluttered with 'unfinished business' - a particularly undesirable state in view of the safety-critical nature of police business. Fig. 5 shows the prototype DS 3000 screen. The

screen is divided into 5 zones. At the bottom of the screen there are two zones for the radio channels and the telephone lines, respectively. The buttons in these areas provide direct access to the corresponding channel or line, and represent the fundamental functionality of the terminal. The two communications zones are never covered by dialogue boxes or other over-writes. Above these zones is a line of buttons

controlling the states of the radio channels and the telephone lines. At the top of a screen is a line of buttons providing access to further, secondary or less frequently used functionality. Between the two rows of buttons is a zone in which dialogue boxes appear, and in which interactions at lower levels in the system take place.

7. Documentation and specification

A task based tool, developed in-house, called a task action description (TAD) was used for the pur- poses of documenting the dialogue design. It de- scribes the system states and the transitions between them in terms of user actions and system responses. The form of the TAD was designed to be transferred directly onto state transition diagrams, which was the preferred tool used by the software engineers in the team. Thus, the TAD is tailored to its users, namely the software engineers.

The concept of the TAD is derived from the principle, put forward by Brigham (1990), that in order to create a dialogue, information is required about the user's tasks, the knowledge required to perform each task, and the actions required to carry them out. The structure of the whole TAD is based

Fig. 5. The prototype DS 3000 screen.

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on the ideas of hierarchical task analysis developed originally by Annett and Duncan (1967) (Annett et al. (1971); see Stammers, in press), in which the operators tasks are divided into a number of sub- sidiary objectives and actions required in order to achieve them. An essential difference between the TAD and task analysis, however, is that tasks are not analysed, but created. The key idea is that the tasks are structured to facilitate the achievement of particular operator goals in a manner which is consistent with the operators' working practices and expecta- tions.

The TAD uses a top-down approach to the design of interactions. The first step is to consider, in

general terms, what it is the user is trying to achieve. This step is technology free in order to enable the consideration of novel solutions. In the case of the DS 3000, this possibility was limited, in that a decision had already been made to use touch screen technology. Nevertheless, obtaining an understanding of the operators' primary responsibilities was fundamental to structuring the interface within this context.

Using the basic concept for the interaction, the operations to be performed in achieving the overall goals are identified. An important aspect of this is to consider how the user will know what to do (the 'Knowledge' part of Brigham's Task Action Knowl-

1.2.6

1.2.6.

"Dial" telephone number.

1 Dial automatically from directory.

SYSTEM STATE: Number in directory required visible. No calls in progress.

OPERATOR ACTION: Press number required. SYSTEM RESPONSE: Number highlighted. OPERATOR ACTION: Press dial button. SYSTEM RESPONSE: Number dialled automatically and connection made. OPERATOR ACTION: Press directories button. SYSTEM RESPONSE: Directory removed from screen.

1.2.6.2 Dial manually from keypad.

SYSTEM STATE: NO calls in progress. OPERATOR ACTION: Press telephone group button. SYSTEM RESPONSE: Keypad dialogue box appears.

Dial tone heard via headphones. OPERATOR ACTION: Press numbers in sequence. SYSTEM RESPONSE: Telephone number displayed. OPERATOR ACTION: Press dial button. SYSTEM RESPONSE: Connection made.

Telephone group button indicates call in progress. Dialogue box removed from screen.

If the number to be dialled is incorrect the operator will be able to "edit" it before the connection is to be made; this will be done by pressing a "delete" button to erase the last digit displayed (ie. the last one typed in). Alternatively, he can press a "clear" button which wil l clear the whole display. He will also be able to break off dialling by pressing a cancel button.

Fig. 6. Example of TAD interaction.

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edge Description; (Brigham, 1990)). In the final specification of the DS 3000, however, it was found the TAD need not explicitly express this 'Knowl- edge'; the information was not directly required by software engineers to translate the interaction specification into state transition diagrams.

On the basis of the operations to be performed and the knowledge required to carry them out, the main dialogues are constructed. It does not, however, provide an exhaustive account of all possible interactions with the system. An example of an interaction as described by the TAD is shown in Fig. 6.

The TAD enabled a clear task focus to be maintained during the detailed development of dialogue proposals. The TAD was written in non-technical English with an emphasis on users and their tasks. It was expressed in terms readily understood by software engineers and product managers.

For each of the actions described in the TAD, a corresponding graphic representation was developed in parallel. This progressive build up of the dialogue and the graphic design enabled the members of the team to monitor and control consistency in style and procedures as well as adherence to human factor principles, such as response time, feedback and status information.

The TAD has two major disadvantages: 1. It can be unwieldy for complex systems. There

are so many potential goals that a great deal of repetition would be required in order to document every conceivable objective the operators may have.

2. It is difficult to document alternative paths, particularly the handling of errors. For this reason, rather than using the TAD to

specify the complete interaction, it was used to document the primary tasks, and this then served as the foundation for the interaction concept. Once this was achieved, in the later stages of the project a more 'traditional' approach was adopted, in which the system reaction to every operator action in every state was documented.

8. Evaluating the design

Within the constraints of this development a for- mal usability evaluation involving performance mea-

surement was not feasible. A more qualitative approach was taken to obtain reactions from operators and potential customers to the design.

A prototype version of the system was taken to a police control centre and demonstrated to the operators on duty at the time. The functionality and design of the terminal was discussed with the operators during this demonstration. Their reactions were very positive, and they were particularly impressed with the restful design and the quality of the interaction and control.

The operators' criticisms were primarily directed at the appearance of the screens. They found the extensive use of grey colouring to be depressing. The final version of the design therefore made use of colour tones in the grey, giving the screens a somewhat richer atmosphere, without detracting from the generally soft approach to colouring, and without compromising the colour coding used. A further desire expressed by operators was to personalise the screens in terms of colour. This was achieved by enabling operators to choose from a number of 'colour schemes' in which the tones of the background colours were changed without interfering with the colour coding used for specific functional attributes.

Operators also criticised the high degree of functionality, which they did not think was necessary. It was not, however, possible to reduce the system's functionality, due to the need to conform to the Smith Associates specification. Functions thought by operators to be unimportant were, therefore, not eliminated, but placed at lower levels in the system structure.

The feedback from operators also made it possible to implement a number of changes of detail in the design, for example, the automatic implementation of particular functions in certain system states (e.g. 'talk-through' when radio channels are connected). It was also possible to change some of the terminology so that it better matched the operators' understanding.

The final design is illustrated in Fig. 7. This shows that the design has matured, both in terms of the sophistication of the screen graphics, and in terms of tailoring it according to the feedback from operators. It can be seen that the basic division of the screen into zones for communication, control and further interactions was retained. Similarly, the oper-

B. Thomas, L McClel land/ lnternational Journal of bTdustrial Ergonomics 18 (1996) 1-13 I I

Fig. 7. The final design of the DS 3000.

ations themselves kept their basic structure, but were refined to better meet the operators' work patterns.

9. Customer and user feedback

The design of the DS 3000 has received a very positive response at a number of exhibitions including the International Police Exhibition and Confer- ence (IPEC) and Telecom 91. It has now been sold to a large number of police forces and other private communications operators. It has, in the opinion of the development manager, significantly enhanced Philips' presence in the market of such products.

The DS 3000 has not been formally evaluated from the human factors point of view in its operational setting. In the context of studies for the development of other equipment for police use, a col-

league was able to speak to some representatives of police forces where the DS 3000 was in operational use (Hartevelt, 1995). These people reported a high level of operator satisfaction, but there are some points of criticism. Many of these criticisms reflect problems of the implementation rather than the design per se, for example, it takes too long for the feedback that an action has been taken to be displayed on the screen. Nevertheless, the general opinion seemed to be that the DS 3000 met the operators' needs better than any other system to date.

In the context of consultancy work in control rooms not related specifically to Philips development activities, Wood (1993) has reported that the DS 3000 has received a very positive response where he has encountered it. He noted this as an example of good ergonomic design in his 1994 Ergonomics So- ciety Lecture (Wood, 1994).

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A more extensive appraisal was made by Lambley (1994), who looked specifically at the use of the new communications equipment by Kent police, which includes the DS 3000. He argues that the DS 3000 has led to a great reduction in stress levels in the control room. The atmosphere in the control room has become so peaceful that " i t ' s as though there's nothing going on" even when 13 incidents are being dealt with at one time. The system manager is quoted as saying that the operators feel more involved, "They ' re all informed, they know what everybody's doing and they have better control." Lambley con- cludes that despite a very complex radio infrastruc- ture at Kent police, the touch screen control system gives it its power.

10. Conclusions

The success of this design is largely attributable to the close working relationships developed between the members of the development team, and clearly shows the benefits of integrating effort in design, human factors, engineering and marketing. The visits to the communications centres enabled a shared understanding and provided foundations for close team work at later stages of the design.

The seamless match between the conceptual model, the dialogue structure, the underlying software and the graphic design could only be achieved through a very close cooperation between graphic designers, ergonomists, software engineers and marketing experts. In order to foster this cooperation, it proved necessary for the members of the development team to meet almost every week to discuss the design details, in spite of the fact that members of the team were located in different countries (the UK and the Netherlands). The level of cooperation achieved also enabled the designers and ergonomists to understand the utility to the operators of the underlying radio and telephone technologies, as well as the digital switching technology. This was necessary in order sensibly to utilise the potential of the technologies and to find ways of circumventing some of the limitations.

A major factor in the success of this project was the attitude of our commercial and technical colleagues with whom we collaborated. They all recog-

nised that the traditional relationship with their customer base was not sufficient or appropriate, and that new approaches to deal with customer and user issues were required. This openness gave us the opportunity to be more adventurous with the intro- duction of new approaches than we might otherwise have been. We want to highlight 3 issues. 1. The importance of direct first hand exposure to

the daily working environment of the operators by the team as a whole. Sharing this experience had, in our perception, a significant influence on later design discussions. It became much easier to deal with 'abstract' operator issues because we were able to refer back to concrete examples. In this respect, the ergonomist played the important role of mediator in exposing the design team to the realities of the operator experience. We strongly recommend that ergonomists advocate sharing site visits, and other opportunities for direct user contact, with the complete design team.

2. The problem of how to articulate operator requirements in such a form that they are taken into account in the design development. Historically ergonomists have relied on specifying user requirements, developing general design guidelines (including prescriptive requirements such as stan- dards), and (more recently) setting usability crite- ria and evaluating the conformance of solutions. All these measures have their role. They are legitimate and necessary but, in our opinion, not sufficient. Ergonomists should share in the responsibility for ensuring that specific design decisions take proper account of general human |:ac- tors dialogue principles (see also Chapanis and Budurka, 1990). To do this, we developed the task action description. The TAD enabled a task focussed dialogue description to be directly cou- pled to a screen graphics specification and the building of the prototype. These 3 activities developed interdependently, and the tools played an additional and important role of providing the 'glue' that enabled the design team to communi- cate effectively.

3. The progressive evolution of organisations and changes in work practices. Adopting the ways of working described in this paper are still not commonplace. For them to become commonplace means significant changes to the way individual

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professionals work together in design teams and, at a higher level, changes to the 'rules' that guide product development programmes (see Gould, 1988). Acceptance and the implementation of such changes at a working level means that the changes will be required in the objectives that guide those who have to take executive responsibility for design decisions. Fundamentally this is not a 'design' issue. It is a process management issue. Ergonomists also have to understand the process issues if user centred design strategies are put into place, and so enable the success we enjoyed with the DS 3000 to be repeated many times over.

Acknowledgements

The work reported in this paper would not have been possible without lhe cooperative spirit shown by our professional colleagues. We would like to acknowledge, in particular, the contribution made by Kathleen Holman and Ingrid van der Zon (designers), Simon Foreman and Ralph Slattery (engineers), and Steve Johnson (product manager).

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