Ergonomics: designing for the userDavid Whitfield, M.A., M.Sc.

Indexing terms: Project and production engineering, Design

Abstract: The aim of ergonomics in design is to maximise the human contribution to system performance,and to ensure that users are not overloaded in their activities. The optimum 'allocation of functions' betweenthe users and the rest of the system must be achieved, and the user-system interface must be compatible withhuman capabilities and limitations. Task descriptions, and approaches to modelling user behaviour, help inthis. Both the hardware interface and the software interface are important in computer-based systems. Otheraspects of system design with substantial ergonomics content are procedural aids, the workspace and environ-mental aspects. Good ergonomics practice demands comprehensive consideration of all the facets of humaninteraction with the system.

1 Who is the user, and why is he important in design?

Many design decisions must take into account the needs andrequirements of the human users involved; this is the provinceof ergonomics. The user may be the operator of the equipmentor system during normal circumstances, the maintenancespecialist who has to deal with unexpected situations, thecommissioning team responsible for a large system, andindeed anyone who will be relying on the equipment (perhapsfrom the managing director using his desk-top computerto the consumer with his new piece of household apparatus).In all these respects, the designer is called upon to act asif he were in the user's shoes, to examine the various waysin which the user will be interacting with the equipment.It may be argued that users are adaptable, and certainly therange of adaptability of human beings is quite impressive,an attribute which may account for the ways in which humanbeings have put up with rather inadequate designs over manyyears. However, exploiting human adaptability in this wayalways increases the workload on the user, and inevitablybrings nearer the possibility of human errors having an import-ant impact on the overall operation of the system. For allthese reasons, and for the basic principle that machines andsystems are, after all, designed to serve human purposes,the designer has a definite responsibility to take into accounthuman capabilities and limitations in his design activities.

There are many cases on record which testify to the import-ance of ergonomics in design. The phrase 'design inducederrors' is becoming more frequent in reports of accidentsin process control systems and in other areas such as flight-deck design. There is an increasing acknowledgement thathighly mechanised and highJy automated systems do notreduce the requirement for the involvement of human oper-ators, but that the demands on the operators are likely to bedifferent and probably rather more complex than before.The human operator is very likely to play the part of a 'super-visor' during normal operation, and to have the responsibilityof detecting adverse trends in equipment or system perform-ance, and certainly in diagnosing and correcting faults. Inall these ways, new technology certainly changes humaninvolvement, but may well increase the psychological demandson the users involved. Another reason for the importanceof ergonomics considerations in contemporary design activityis that technology in all its aspects is now advanced andflexible enough to be able to meet human requirements:the tremendous improvements in display and control facilitieswhich have taken place over the last 20 years have providedthe designer with the means for really successful accommo-dation of the particular requirements of users.

Paper 25S4A, received 10th Juanuary 1983The author is with the Ergonomics Development Unit, University ofAston in Birmingham, Kyrle Hall, Gosta Green, Birmingham B4 7ET,England

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Thus ergonomics approaches design from the point ofview of the capabilities and limitations of the human operatorsinvolved. The designer should take these human characteristicsas his starting point, and then proceed to make his designdecisions in accordance with those features. Good designshould aim to make the best use of the peculiar skills of thehuman operator, while ensuring that he is not overloadedeither mentally or physically. In more formal terms, the dualobjectives of ergonomics are to maximise the human contri-bution to system performance and to ensure that the wellbeing of the operators is preserved. The principles and practiceof ergonomics are derived from several areas of theory andresearch in the human sciences, and the benefits of applyingergonomics can be demonstrated in examples such as thereduction of human error rates by designing equipment andsystems in accordance with human characteristics.

Some books and papers which may be of use to thedesigner are listed at the end of this paper, but it must beemphasised that much of ergonomics is not suitable forapplication direct from a data sheet or from a text book.Human behaviour is influenced by a very large number ofvariables, and even basic data may require careful interpret-ation. As an example, digital presentation of numerical infor-mation has been shown to be beneficial in applications suchas micrometers or machine tool indications, whereas it isrecommended that aircraft altimeters should have digitaland analogue presentation. In these cases, the distinctionsbetween the shop-floor and flight-deck tasks are intuitivelyobvious: the former requires discrete observations with highaccuracy, while the latter involves also elements of a continu-ous 'tracking' task, where rate of change information isespecially important. In other situations, the salient featuresof the human operator's task may be more difficult to define,and it is here that the ergonomist makes a special contributionto equipment and system design, with his techniques fortask description, as outlined in Section 3. Thus this brief paperis concerned mainly with general approaches to operatoractivities, rather than with the extensive and detailed dataand recommendations available in the standard literature.It cannot be overemphasised that the application of suchdata must be guided by a complete understanding of theuser's task and of his requirements and limitations.

2 Integrating user and system

The designer is aiming to achieve the most effective compati-bility between the human beings and the rest of the system.One fundamental stage in the design is to allocate responsi-bility between operators and the other system components.The required functions have to be allocated between manand machine, so as to ensure the overall success and efficiencyof the system. This is a difficult design stage, and there areno rigorous techniques for solving it, but we can define

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some general criteria. First, in terms of the system consider-ations, we can consider the relative abilities of men andmachines. In general terms, machines (including computerdevices) are best for performing activities which can be speci-fied precisely, for they surpass man in terms of speed andreliability. On the other hand, man has advantages in tasksinvolving inference and extrapolation, pattern recognition,and decision making under uncertainty. Secondly, in additionto relative abilities, consideration must be given to cost/effectiveness: the effectiveness of an automatic monitoringdevice may be high, but is it justified in relation to the costof designing, developing, building and maintaining the device?Cost/effectiveness measures are certainly not always in favourof the human operator, but his attractive features includeflexibility and multipurpose qualities, the capacity to'reprogram' for new circumstances, and a large store of pastexperience of system operation. Thirdly, the human shouldbe presented with integrated tasks, i.e. tasks which are coher-ent and relatively complete, and which make a significantcontribution to the whole system. Such tasks produce ahigher level of motivation than fragmentary tasks, but, evenmore important, the operator will be able to develop andmaintain his special abilities only under the conditions ofintegrated tasks. The process plant controller is able to adaptto unusual plant behaviour, to predict future situations fromthe current state of the plant and to integrate informationfrom a number of sources, only if he has regular practicewith the system itself. Thus in fault conditions the operatorwith extensive and regular tasks can react more quickly andmore efficiently than an operator who is thrust suddenlyinto the system by a general alarm.

Current and future developments in computer technologymake the allocation of functions stage even more crucialand complex. For a start, there is essentially a tripartiteallocation: to human, to hardware or to software. Then thecapabilities of computer-based systems are increasing apace,and, in principle, more functions can be taken over from thehuman operator. However, the human requirements forintegrated tasks, for maintaining complex skills and for com-prehending system operations all remain. In many situations,the concept of the computer contribution as an aid or decisionsupport system for the operator is of considerable value.The system designer presents computer functions to extendthe capabilities of the human user, while leaving him in ulti-mate control and with a comprehensive understanding ofsystem operation.

The allocation of functions between the user and therest of the system defines the 'man-machine interface', andthe designer must then ensure that the most efficient com-munication is possible across this interface. Display andcontrol devices must be designed in accordance with humancharacteristics for receiving information and implementingactions, the various components of the interface must bearranged in a workspace which allows the best vision ofdisplays and the most convenient access to controls, and thegeneral environmental conditions must promote the efficientexecution of the human tasks.

Concern with the man-machine interface in the past haslargely concentrated on hardware aspects, and the literaturecontains many recommendations on these aspects of displayand control elements. More recently, the interface withsystem software has become important, and the designeroften has to become involved with the layout of computergenerated displays, the detailed design of the 'dialogue'between operator and computer, and with the provisionand design of various types of support documentation. Theseareas are often referred to as 'cognitive ergonomics', as theyput even more emphasis on the psychological capabilities

of the operator than was the case where recommendationswere being made for hard-wired devices.

3 The need for task descriptions

It has been emphasised already that the nature of the oper-ator's task will have a profound effect on the ergonomicsaspects of design. The sources of information on which tobase a task description are various: existing or similar systemscan be observed, and their operators can be interviewed,while new systems may have documented procedures andsets of activities. The means of representing a task descriptionare similarly varied: block diagrams, flow charts, signal flowgraphs, tabular listings and matrices may be employed whererelevant. The important feature is that operator tasks areexamined objectively, and most presentations are based oninformation/decision/action/feedback elements of the task.In whatever form, the task description is a specificationfor human involvement with the system, and it ensures thedesigner's understanding of the human operations, as thebasis for his further design decisions on detailed aspects ofthe interrelationship between operators and system.

The 'decision' element is the fundamental considerationfor the designer: it specifies the actual contribution of theuser at that point, and it gives an indication of the difficultyand complexity of this particular segment of the task. The'information' element must provide the basis for makingthe decision, and it has implications for the selection andpresentation of material on displays. 'Action' sets the require-ments for control and manipulation devices, while the 'feed-back' element will specify the need for displays and controlsto give sufficient indication of the effects of an action, sothat the operator can work in closed-loop mode, as is thetypical case.

As well as specifying requirements for individual displayand control elements, the task description gives the overallpicture of sequences of activities, and recurring patterns,all of which have implications for the organisation of theuser's activities and the design of his equipment.

4 Models of the user

It is natural that the designer should ask for models of theuser, as models of other system components are generallyavailable, as in stress analysis, and circuit design. The user'sanatomical and physiological characteristics are fairly easilyrepresented, as is discussed in Section 7. His psychological,or information-processing and decision-making, capacitiesare rather more complex. Sheridan and Ferrell [1] presentreviews of models based on information theory, decisiontheory and control theory, respectively. It is fortunate thatmodelling of human performance is based increasingly onsuch concepts, which are familiar to the engineering designer.However, it has to be admitted that such models are oftenonly first approximations to true representations, and arerestricted to rather specific areas of tasks. Control theorymodels have been most successful to date, in dealing withhuman interaction with vehicle control, particularly aircraft:the optimal control model is a highly developed area [2].

Other mathematical models are applied in certain typesof task. Rouse [3] presents a contemporary review, includingtopics of queueing theory, fuzzy sets and stochastic processes.In most cases, the models act as prompts for general inquiry,as opposed to precise predictions of human performance.Nevertheless, they enable the system designer to make someanalytical approaches to man-machine interaction.

Another recent development, which can be regarded asa type of model, is the consideration of human reliability.Reliability analyses of high-risk plant and equipment are now

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common, and it is acknowledged that the contribution of thehuman operator is crucial in certain operational situations.Thus there is considerable interest in human reliability, or,to put it another way, in human error. The various typesof human error are analysed and tabulated (see, for example,Reference 4), and such categorisations suggest vulnerableaspects of task descriptions. Many of the ergonomics designrecommendations will have the effect of reducing the prob-ability of human error, and there are some developing tech-niques which will yield data for quantitative prediction ofhuman reliability. As always, a detailed task descriptionis essential: the availability of quantitative data on individualtask elements is very limited, and there is controversy overthe methods for defining task elements and aggregating them.Further advances are required in these techniques: for thepresent, the emphasis on human error and its consequencesis important for the designer.

5 User-system interface

An interface allows communication. Between the user andthe system, display devices convey information from theprocess to the human, and his consequent actions and com-mands are returned to the system via control elements. Forefficient communication, this interface comprising displaysand controls should be designed to conform with humancapabilities and limitations. At a detailed level, the generalergonomics textbooks (see, for example, References 5—8)give design recommendations for individual displays andcontrols. Such recommendations include sizes of characterson displays, illumination and contrast requirements, sizesof controls, and so on. However, these detailed designdecisions should be preceded by consideration of the overallorganisation of the system-user information flow.

The structure of the complete panel, or panels, of displaysand controls should help the user to understand the functionsand operations of the complete system. Then the functionalrelationships between specific groups of displays and controlsshould be made clear. The emphasis must be on the operator'sunderstanding of the functions of the system. Particularlywith large-scale instrumentation, the operator has no directcontact with the process which he is monitoring or controlling.The designer's provision of displays and controls gives anartificial representation of the process: it should create thecorrect 'mental model' of the process for the operator. Thedesigner must not allow his own familiarity with the tasksto blind him to the operator's relative unfamiliarity and toomit aids to understanding or developing a mental model.The tasks have to be analysed from the operator's point ofview, and in relation to the likely levels of his skill and experi-ence.

In display design, the aim should be to reduce the oper-ator's information load by using the simplest type of displaywhich is compatible with task requirements. As far as visualdisplays are concerned, we distinguish between four majorcategories:

(a) Qualitative: indication of one or more of a small num-ber of possible conditions or events. Simple devices, such asindicator lamps, are adequate for this purpose. Unambiguousidentification of the information is aided by 'coding' interms of the position, shape, colour and size of indicators.

(b) Analogue: presentation of numerical information,on conventional scale and pointer instruments, or on graphicalor semigraphical computer-generated displays. Analoguedisplays enable fairly rapid, approximate, interpretation,and they can be designed to convey patterns or configurationsof data arrays, for example in depicting trends or rates ofchange in parameters.

(c) Alphanumeric: as in (b), the presentation of detailedinformation, often numerical. Alphanumeric displays enablethe user to make more precise readings, because there isno need for interpolation on an analogue scale. However,with VDU presentation rather than individual alphanumericdisplays, there is a real danger of swamping the user withtoo much information. Nowhere is this more obvious thanwith computer print-out: ergonomics principles can be appliedto these 'static' displays as well as to 'dynamic' VDU formats.The amount of information presented must be controlled,and the arrangement of the screen format must reflect theuser's needs and the organisation of his task.

(d) Representational: here, the display presents a schematicor mimic diagram of a segment of the plant or process. Theaim is to develop and maintain the user's 'mental model',as discussed above. Representational displays may beassembled from hard-wired conventional instruments, or theymay be implemented on more or less sophisticated computergenerated displays. Certainly, the latter provide increasingflexibility, and the use of colour, for example; however,the same danger of information overload, and the need torelate to the user's mental model, still apply.

In control design, most applications will provide the userwith hand, rather than foot, controls. The textbooks containdetailed recommendations on the choice of control (thepossible candidates include knobs, levers, switches, push-buttons, joysticks, touch-screens, tracker balls, keyboardsetc.) and on mechanical characteristics, such as size, shape,spacing, operating forces, friction and damping. As withdisplays, the control should suit the task: a basic distinctionis between continuously variable adjustment and discreteselection. A control knob or lever may be best for the former,while the latter may involve push-buttons or switches: thusthe required nature of the action is made clear to the user.

Controls have broader aspects also. The provision of feed-back to the user has been mentioned earlier: the controlmust provide sufficient 'on-line' feedback to enable the userto monitor and adjust his actions, and it must display itsstate or position as required, for purposes of checking controlsettings (in this respect, a control nearly always incorporatessome display aspects). For continuously variable controls,there may be a close relationship with a display where thecontrolled parameter is presented: the relationship can bereinforced by close and consistent positioning of controlsand displays on equipment, and by careful choice of move-ment relationships between them. Extensive research hasshown that operators expect certain control-display move-ments to occur, and their performance is disrupted, particu-larly under emergency or stress conditions, if these expec-tations are not incorporated in equipment design. This is asimple example of a user's mental model of equipment oper-ation. Finally, control-display dynamics may be importantin some specialised applications: a zero-order or positionalrelationship will be adequate for most purposes, but higher-order (velocity, acceleration etc.) may be inherent in, orrequired for, skilled tracking tasks (see, for example, Refer-ence 9).

The control element in the user-computer interface mayinvolve any of the control devices mentioned above, butthe ubiquitous QWERTY standard typewriter keyboard willoften appear to be necessary. Alden et al. [10] review thebasic ergonomics aspects of keyboard design. There is nodoubt that the standard keyboard is a difficult interface forusers who possess little typing skill, and feasible alternativesshould always be explored. Custom-designed dedicated key-boards may be the solution in some cases. A more flexiblearrangement is the 'virtual keyboard' defined on a computer -

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generated display and accessed by the user directly (usingsome type of touch screen) or indirectly with an off-screendevice (see, for example, References 11 and 12). The use ofvirtual keyboards and other types of interaction, such asmenu-selection, are particularly appropriate to nontypist users.

The software interface has been mentioned already. Thehardware devices which are the vehicles of communicationbetween user and computer system are fairly well definedfrom the ergonomics point of view, but the user-computerdialogue is only a relatively recent area of interest. Thereare many aspects, such as the design of command languages,the structure of menu access systems, and the representationof computer procedures, where ergonomics principles andrecommendations are being developed (see, for example,References 13 and 14).

6 Procedural aids

Much of ergonomics puts emphasis on information whichis supplied to the user through dynamic displays, as describedin the previous Section. An equally important type of infor-mation for users, and one which is overlooked often in systemdesign, is 'static' information on procedures to be followedin various operations. Such information sources includeinstruction manuals or handbooks, check-lists, calibrationcharts, computational aids, diagrams and charts. In any com-prehensive approach to man-machine systems, this area ofinformation must be analysed and designed, with the taskrequirements and operator characteristics as the frame ofreference. Evidence of the importance of such proceduralaids, particularly in reducing user errors, is not hard to find.Vandenberg [15] gives one dramatic example: the dockingfailure of the US Gemini 9 satellite, a $900000 loss, wasascribed to a badly written set of procedures in an installationmanual. In everyday situations, similar inadequacies areevident: the operation manual for a piece of laboratoryequipment which complicates the description of normalprocedures by introducing too much technical detail, or thecar maintenance manual which provides too little informationfor the average user. This aspect is probably one of the mostimportant. Commissioning, routine operation and maintenancework each involve users of different levels of training andunderstanding of the system, and the task demands vary also.Thus the procedural information must be selected anddesigned appropriately for each context.

Wright [16, 17] has discussed the 'quality control ofdocument design'. She distinguishes the successive stagesof content (what should be said?), presentation (how shouldit be said?), and usability (can it be used adequately by thereader?). In addition to the central role of the task descriptionin determining content, she emphasises that technical docu-ments are usually intended for information searching, asopposed to being read from cover to cover. There may alsobe very important decisions on what information shouldnot be included, as well as what should. The designer ofprocedural aids can, and should, involve users and potentialusers of the system in these decisions: as in other aspectsof system design, operator consultation and involvementcan be productive.

Many manuals will rely heavily on prose, and Wrighthas discussed general recommendations for improving thecomprehensibility of technical prose. The recommendationsmay not apply in all circumstances, but they will usuallyease the reader's task. Sentences should be:

(i) short, but not cryptic(ii) simple, without subordinate clauses

(iii) active: the passive voice may hinder comprehension(iv) affirmative: negatives may hinder comprehension.

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Again, in many situations, continuous prose may be avoidedaltogether. The use of algorithms for presenting routinesets of actions and operations, with clearly presented decisionpoints, can confer considerable benefits (see, for example,Reference 18). The algorithmic format gives an explicitpresentation of information and decisions, and sets out therequired decisions in a logical order.

The use of illustrative material, such as diagrams andcharts, is also a very effective alternative to prose: 'Onepicture is worth a thousand words'. Tables, graphs and nomo-grams are equally effective in condensing numerical infor-mation. Much of the detailed ergonomics recommendationson display design can be applied to all these media. Moregenerally, there is often the opportunity to simplify thetechnical material presented on fault-finding diagrams:'functional' diagrams which concentrate on a generaldescriptive level, rather than presenting very detailed technicaldata, may be more effective in the early stages of diagnosis.

Alphanumeric codes have received some ergonomics atten-tion, and they become increasingly important in computer-based systems. From the user's point of view, the typicalrequirement is to hold the code in short-term memory fora few seconds, as in cross-checking between two documents,and research yields the following general recommendations:

{a) Length: increasing length causes more errors, andparticularly with more than six or seven characters. However,longer codes can be made easier by these further techniques.

(b) Grouping: preferably into sets of three characters,for example 907-354-261 instead of 907354261.

(c) Letters: although digits tend to be easier to rememberthan letters, convenient mnemonics, such as PRE or CAL,are very helpful.

(d) Structure by digits and letters: codes are more easilyhandled when there are separate groups of digits and letters,for example PRE 490 rather than P4R 9E0. Any other regularpatterning of letters and digits will be helpful also.

7 The physical environment

The designer's influence over the physical environment ofthe user will vary, depending on his brief. If he is responsiblefor the design of a complete central control room for a processplant, then he will have to make decisions on all these aspects,or at least he will be involved with a design team which hasthese broad responsibilities. At the other extreme, he maybe working on a small item of equipment, to be mass-producedfor a variety of applications and settings. In that case, onlythe most immediate aspects of the work-space will be underhis control, although it could be argued that he should makerecommendations for the eventual users' choices of, say,lighting conditions under which the equipment will be used.

The work-space is the most immediate aspect of theenvironment: the arrangement and dimensioning of the largeraspects of the user-system interface, including the size ofcontrol desks or operating consoles, access to control panels,and visibility of displays from the user's normal workingpositions. All these aspects must suit the appropriate humanbody measurements, data on which are available in theergonomics literature (see, for example, Reference 19).The data used must be from the relevant population, andmaximum or minimum values, rather than the average, arenecessary for certain aspects. A drawing-board analysis basedon such data is a first step, but the complexities of body andlimb movement in three dimensions make it desirable totest out adjustable full-scale mock-ups with large and smallrepresentative users (chosen by reference to body-measure-ment tables). A full scale mock-up enables problems of accessand visibility to be evaluated, along with 'walk-through'

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assessment of the general arrangement of controls and dis-plays. Computer-aided design packages are available to extenddrawing-board analyses to an interactive modelling of thethree-dimensional situation (see, for example, Reference 20).The CAD package may have the facility to present the user'seye view of the equipment during its operation.

The ergonomics literature contains specific recommen-dations for the thermal, lighting, noise and vibration con-ditions in which the user works. Perhaps the most difficultitem in many situations will be lighting. The maintenanceof adequate illumination levels on all working areas, withoutglare or specular reflection on display surfaces (with VDUs,the screen s'urface and upper surfaces of the keys are particu-larly vulnerable), demands careful planning of the wholelighting sytem. As mentioned above, even where the designerhas no control over individual installations, recommendationson lighting should be supplied with the equipment.

8 Conclusion

This short paper has tried to set out the concerns of ergonom-ics, as comprehensively as possible, to draw the designer'sattention to a properly integrated approach to the user.Starting from a suitably detailed task description for the user,the designer has a responsibility to consider all these facets,and their inevitable interactions.

) References

1 SHERIDAN, T.B., and FERRELL, W.R.: 'Man-machine systems:Information, control and decision models of human performance'(MIT Press, 1974)

2 BARON, S., and LEVISON, W.H.: 'The optimal control model:Status and future directions'. Proceedings of IEEE Conference onCybernetics and Society, Cambridge, MA, USA, Oct. 1980

3 ROUSE, W.B.: 'Systems engineering models of human-machineinteraction' (North-Holland, 1980)

4 SHERIDAN, T.B.: 'Understanding human error and aiding humandiagnostic behaviour in nuclear power plants', in RASMUSSEN, J.and ROUSE, W.B.: 'Human detection and diagnosis of systemfailures' (Plenum, 1981)

5 McCORMICK, E.J., and SANDERS, M.S.: 'Human factors inengineering and design' (McGraw-Hill, 1982), 5th Edn.

6 SHACKEL, B. (Ed.): 'Applied ergonomics handbook' (IPC, 1974)7 SINGLETON, W.T.: 'Introduction to ergonomics' (World Health

Organisation, 1972)8 WOODSON, W.E.: 'Human factors design handbook' (McGraw-Hill,

1981)9 POULTON, E.C.: 'Tracking skill and manual control' (Academic

Press, 1974)10 ALDEN, D.G., DANIELS, R.W., and KANARICK, A.F.: 'Keyboard

design and operation - a review of the major issues', Human factors,1972, 14, pp. 275-294

11 BALL, R.G., NEWTON, R.S., and WHITFIELD, D.: 'Developmentof an off-display, high resolution, direct touch input device: theRSRE Touchpad', Displays, 1980, 1, pp. 203-207

12 USHER, D.M.: 'A touch-sensitive VDU compared with a computer-aided keypad for controlling power generating plant'. IEE Conf.Publ 212, 1982, pp. 250-253

13 SHACKEL, B. (Ed.): Man/computer communication. Vols. 1 and2' (State of the Art Report) (Infotech, 1979)

14 National Bureau of Standards/Association for Computing Machinery:Proceedings of Conference on Human Factors in Computer Sys-tems, Gaithersburg, MD, USA, Mar. 1982

15 VANDENBERG, J.D.: 'Improved operating procedure manuals',Ergonomics, 1967, 10, pp. 214-220

16 WRIGHT, P.: 'Presenting technical information: a survey of researchfindings', Instructional Sci., 1977, 6, pp. 93-134

17 WRIGHT, P.: 'The quality control of document design', Infor-mation Des. J., 1979, 1, pp. 33-42

18 LEWIS, B.N., HORABIN, I.S., and GANE, C.P.: 'Flow charts,logical trees and algorithms for rules and regulations' (HMSO,1967)

19 DIFFRIENT, N., TILLEY, A.R., and HARMAN, D.: 'Humanscale:A portfolio of information' (MIT Press, 1981)

20 CASE, K., and PORTER, M.: 'SAMMIE - A computer-aidedergonomics design system', Engineering, 1980, Jan., pp. 21-25

David Whitfield had his initial profes-sional experience as ergonomist in anelectronics company, working on civiland defence systems, and from researchin human skills and ergonomics at theCollege of Aeronautics, Cranfield. He thenbecame a Research Fellow and laterSenior Lecturer in applied psychology atthe University of Aston in Birmingham.At Aston, he founded the ErgonomicsDevelopment Unit, which undertakes

contract systems research for a variety of organisations. He isan Associate of the British Psychological Society, a Memberof the Ergonomics Society and a Fellow of the Human FactorsSociety (USA).

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