-lr The prototype computer. 2 The latest veÍsion redesigned 'l t

Iaccording to ergonomic principles. uexen E M I Electronics Ltd.

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reset from one problem to solve another; ease ofopera-

tion and avoidance of operator mistakes are therefore

essential. Such mistakes are far more troublesome than

loss of speed or machine inaccuracy' A correct setting,

but on a wrong potentiometer - or a switch left in the

wrong position - can ruin the solution of a problem

and cause much delay while the fault is found. Even

worse, the error in the solution may not be discovered.

Therefore the risk of these mistakes must be reduced

to the minimum by proper attention to ergonomlc

factors.

During the redesign of EMIAC II, at EMI Elec-

tronics Ltd, advice from the firm's engineering

psychology laboratory was sought on various aspects of

the operational layout; the prototype, r, was already

fairly satisfactory, but the project team wished to make

every possible improvement.

Ergonomics

for a,

Gomputer

AN ANALocuE coMPUTER is an assembly of many,

similar, electronic 'building bricks' which can be con-

nected together in a multitude of different ways. The

input and output leads of the amplifiers, integrators,

and function potentiometers are all brought out sepa-

rately to sockets on the 'patch panel', which is thus very

similar to a telephone exchange switchboard. By mak-

ing the appropriate interconnections the operator can'patch up' the computer to solve most problems which

can be defined in suitable mathematical terms.

Analogue computers are particularly useful to simu-

late and optimize the design and working of complex

devices with several interdependent variables, such as

suspension systems of motor cars or chemical pro-

cessing factories with continuous flow.

Flexibility is an important feature of an analogue

computer, so that it can quickly and accurately be

DÉSIGN I2O

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ElïfIAC

II

Potentiometer panelThe major problem in this study was the panel of z4 potentio-

meters, all of which may have to be selected one at a time by an

appropriate switch and adjusted very carefully to an exact value

on the meter. Unless the layout is clear and simple, there is a risk

of setting up the wrong potentiometer or of starting to adiust one

which has already been set, with consequent annoyance and risk

of error.

On the prototype, to economise in space, the potentiometers

were staggered at 45" to each other and the jack sockets, through

which electrical connection is made to the potentiometers' were

set in between them. The result is somewhat confusing and there

is no room for numbers to identify each iack socket, 3. Despite

added electronic complication and slight increase in panel size it

was agreed to use push-pull switches with a number on the knob

to replace the iack sockets; the design problem therefore was to

frnd a layout with which the sequence of operations - frsr, find

and operate the switch, second, frnd the potentiometer, third,

adiust it, and, fourth, turn off the switch - would be done most

easily and with the least error.

The method of tackling this, as with all ergonomic problems, was

DESIGN I2O

f irst to refer to results of all relevant research I ; i t was found, how-

ever, that the evidence in the l iterature was not adequate to allow of

reliable extrapolation to solve the problem. Therefore an expcri-

ment2, had to be made which resulted in the optimum layout, 4.

It was suggested init ially that a rotary selector switch should be

used instead of the iack sockets. This proved impractical electroni-

cally, but the discussion and explanation brought to l ight a way in

which part ofthe basic engineering circuit could be improved. This

is quite a common experience during ergonomic redesign studies;

explaining the machine to someone with a different specialist

approach stimulates the engineering team to reconsider its

system from a fresh viewPoint.

r See for instance: Applied experinental psycholggy,, A. Chapanis'\í. R. Garner and C. T. Mbrgan. Chapman and Hall Ltd, f,z tzs

Hwnan engineering gtide fot equipnent designets' W. E. Woodson' CUP{r 6s .Data on hunpn perJornnnce fot engineeting designers, K. F. H. Murrell'reprint from Ezgineering, 3s

Y'f :{r:if:;o,'"r;9*ÊWÍ,ïi;*h.3X'J""f 8L'Y;i;.51'ïX'H. K. Lewis & Co Ltd, dr Is.

zAnote on Danel layout for nuntbets of ident ical i rerts, B, Shackel, to bepubl ished iÁ Ergononics. Taylor and Francis Ltd continued

I i rgonomics lbr a corntrruler.

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Control panelThc Íull opcrating sequcncc must bc knorvn belbrc clccidirrg rm_portant panel layouts; only bv analysing thc various sub-rourrncscan related controls bc properly grouped together. Crit ical adjust_ments and master controll ing actions arc usuallv made with thcprefened hand (thc right hand for most of the population; andtherefore such conrrols should be placed casily for the right hancl,leaving associatcd less crit ical switchcs to thc leÍi.

It Íbllowcd that the main changc, T ancl g, u,as to intcrchangethe Meter F S D switch and the accuratc potcntiometcr with rhe

graduated d ia l ; p rev ious ly the opcra tor rvou ld tcnd ro opcra tc thcmetcr switch u'ith thc lelt hand, thus obscuring the meter he wasabout to read, so as to use his right hand Íbr crit ical adjustmcnt.Thc master control is Rorv A switch and is thercforc in thc corrccrposition; thc otlter groups of amplif iers are usually undcr itscontrol, and thercfore Row B and Row C switchcs arc in thc lessrmportant corncrs of the pancl. Other changes in dctails improvcthc idcntif ication of su'itch positions and group rclated ircmstogethcr.

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Some time after the study had finishcd an opportunity arose toask the recipient of the prototvpe model, the Hawker SiddeleyNuclear Porvcr Co Ltd, íor crit icisms of its operation. It rvaspleasing, if not unexpected, to find that comments from at leastthree months' operating of the machine had all been predicted byrhe ergonomic redes ign s tudy .

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ConclusionsIn this brief example of how an electronic machine is studied rnorder to improve the ergonomic aspects of its design, only themore obvious points have becn mentioned. To the design engi_neers and technologists, who are at prcsent the chief users of thiskind of machine, some of the more detailed aspects u,i l l beobvious from the i l lustrations,