NICE VERSUS NECESSARY - A DANGEROUS TRAP IN MAN-MACHINE SYSTEM DESIGN

NEWSLETTER ARTICLE

Man-machine system design is often plagued by the same thinking that has become entrenched in the federal government: failing to distinguish what would be nice from what is necessary. Whereas Washington enacts programs/legislation that would benefit some segment of the population—seemingly blind to the basic functions of the federal government and current budgetary limitations—refinery personnel often do the same with features and attributes of the man-machine system.

Beville often encounters features in the design of display systems, procedures, and training programs that are present because they would be "nice for the operator." Often, by themselves, they appear to present no problems, but when aggregated across an entire system, the result is a "bad" man-machine interface. One example is the use of tag numbers with all PV's on a graphic display. It is a "nice" addition, but in many cases is not necessary. The operators often don't rely on the tag numbers and they are available in the change zone if a number needs to be determined. However, including the tag numbers requires twice as much space on the screen versus PV's alone, adding noise to each screen and often increasing the number of displays that must be built and paged through. Another example was a trainer at a refinery who wanted to increase the operators' "knowledge" of the plant. While it has been facetiously said that "Knowledge is Good," the application to operator training results in huge training manuals that require extensive time and effort to keep updated, and may not improve operator performance.

The presentation of information to the operator should be based upon what is necessary. Is the information needed for the operator to perform at the desired level of performance? Other information may be nice, and could be made available, but don't confuse the nice with the necessary. It is important to determine: 1) what is the operator to do, 2) what do they need to know, and 3) what information is needed to perform the task. Keep it simple; less is usually more.

Copyright 1995 Beville Operator Performance Specialists, Inc., All Rights Reserved