How does interface design shape operator performance?

Performance-Shaping Factors Series

NEWSLETTER ARTICLE

Operator performance is a function of numerous interacting variables. This series of newsletters examines each of these variables, or performance-shaping factors (Figure 1).

Lesson 8 – Interface Design

There are dozens of books on interface or display design, and I’m tackling it in a newsletter. My first step was to decide what to leave in, what to leave out (that’s for fellow Bob Seeger fans). This could end up, though, like a history of WWII as reported by grade school kids or the cryptic abbreviations in the old TV Guide (“Germany’s plans for expansion go awry"). So, rather than trying to give specific rules — “If you use the color red for warning, don’t use it for anything else, not even motors being stopped!” — I want to discuss how you approach the task of creating a display SYSTEM rather than a collection of graphics.

Once Upon a Time . . .

Of all the performance-shaping factors, interface design is probably the one most people would cite as having the greatest influence on console operator performance. Unfortunately, most people also think that interface design is all about drawing graphic displays. It’s not. Don Norman, author of Things That Make Us Smart, likened display design to telling a story. I will add that if you are going to tell a story, HAVE A POINT!^[1]

To illustrate: If asked for the story of your life, I hope you don’t just start reciting facts. Hopefully, you will have to think about how you want to organize the events in your life (the tags of your life). While you could do it in chronological order (the equivalent of starting with the P&ID of the feed system), there are certainly more important aspects than what happened the day you were born. If you’ve successfully broken your life into meaningful sections, each of these likely has several underlying themes or points. Taking this sort of deconstructionist approach makes for good storytelling and better display systems.

All the Makings of a Good Story

A technique to facilitate this process is called IDEF. It was developed by the US Air Force with the intent of defining system requirements. It’s surprisingly simple, based upon decomposing tasks. The basic format is the task, which must have a verb (action), the inputs/outputs, any constraints on the task, and the mechanism by which the task is performed. The task is then decomposed into subtasks (typically no more than six). Each task/subtask is potentially a display, the inputs are the information needed, and the decomposition automatically forces the result to be organized into a hierarchy with obvious navigation.

The IDEF for a refinery would have an overall task of separating crude (i.e., the crude unit). That could be broken down into —

1. remove salt,

2. heat crude,

3. distill crude,

4. purify components (i.e., strippers), and

5. distill gas oil (i.e., vacuum column).

These five tasks or nodes would comprise the Level 1 display for the unit. The node for remove salt might look something like this.

Each of these nodes are then further decomposed. As shown below, the task of removing salt from the crude can be further broken down into more tasks. This breakdown creates the Level 2 graphic. Each display is making a point, the task from which it came. The decomposition continues until the system is fully defined (i.e., all instruments accounted for).

~ THE END ~

A story of the process has been defined, with each display making a point, the tasks to support the higher level. Now the graphics can be created to tell the story. The information is organized and structured. The important has been separated from the unimportant by focusing on the tasks the operator needs to perform and identifying the information necessary to do so. This is the major aspect of display system design, the content and organization of the displays. Colors and shapes play a role, but what makes a good display system is that it makes sense, it makes a point.

[1] Martin, Steven. “Planes, Trains, and Automobiles”, 1987

Copyright 2023 Beville Operator Performance Specialists, Inc., All Rights Reserved