Analysis Techniques For Man-Machine Systems Design

NATO UNCLASSIFIEDAC/243(Panel 8')TR/7Volume 2Inputs to the techniqueThe analyst requires information on the sequence andperformance criteria for the opermtor's tasks, and detailsof the human-machine interface design.Outputs of the techniqueCritical task analyses are usually presented as tabulationsof the required information. There is no standard format.Annotated Opcrational Sequence Diagrams are sometimes.used.When to useBecause of the amount of detail required for the analysis, usually it cannot be prepared prior to the design definitionphase of a project It requires input from other task analyses and from an interface design concept. Some usersrecommend that a mock-up of the interface be used as a basis for the analysis, which would determine the schedule ofthe work.RelatedtechniquesCritical task analyses are characterized more by the lcvel of detail of the analysis, than by the specific technique used.The approach is related to Operational Sequence Diagrams (4.3). and to Information/Action tabulations (4.4).ResourcesrequiredDetailed operator task information and details of the human-machine interface are needed. Use of a computer isrecommended, to handle editing and updating.AdvantagesDisadvantagesIn general, users report the technique to be effective. The The level of detail provided can be overwhelming, so thatanalysis is straightforward to conduct, and forces the the reviewer has difficulty understanding the overall patterndesigners to develop a thorough understanding of what of operator activities. Users report that the technique doesthe operators of a system will be required to do. not deal well with parallel, multi-task situations. It isreported to be of medium difficulty, and quite timeconsuming.The time requirement can limit the extent ofapplication of the analysis. Analysts should choose theapplication carefully.Relative contributionSome users find the technique quite effective. One user, however, indicated that it had low effectiveness on theirproject. It has been found very effective for identifying the tests which are to be run in the test & evaluation phase.ApplicationsThe technique has been widely called up in system requirements documents, but there are few reports of its use. It wasused for the development of a European stike aircraft, for a tank, US helicopter system (Parks, 1987), naval sensorsystems, and a naval ship.NATO UNCLASSIFIED- 82 -