06 SCREENS · Displays that think for you
Show the answer, not the parts.
You will learn how to design a display that gives people the answer instead of the parts. It takes 3 minutes.
Are you speeding? You'll need to do math
The limit is 45 mph. Your display shows this:
LIMIT45
Take a few seconds. Are you over the limit?
Show the math you had to do
22 m/s × 2.237 = 49.2 mph
That's a unit conversion, in your head, while driving.
Watch the clip: it does the math for you
The clip runs this example, then a harder one from an airliner cockpit. Watch for the green arrow.
The name for it
THE NAME FOR IT
Human-factors display design
Aviation and spacecraft display design · predictive aiding, minimal mental math
Present information in the form the task needs, so the operator reads an answer instead of calculating one.
Show 49 mph, not 22 m/s
LIMIT45
Same reading. The display did the conversion and the comparison. The driver reads an answer: 4 over.
Show where the speed will be, not only where it is
An airliner is at 250 knots, gaining 1.2 knots a second. The limit is 262. How long until it hits the limit? That's a division, under pressure.
Airliner speed displays solve this with a trend arrow. It points to where the speed will be in 10 seconds. Arrow touches red: you have about 10 seconds. No division.
Do the work once, in the display
Every time a display shows raw parts, every reader does the same math, every time, and some get it wrong. Do it once in the design:
- Convert to the units the task uses. The road sign is in mph, so the display should be too.
- Compare to the limit for them. Put the limit on the scale. "4 over" beats two numbers.
- Predict where it's heading. A trend arrow or a "time to empty" answers the next question before it's asked.
- Put the answer where the eyes already are. Don't send people to another screen for the number that decides.
TAKEAWAY
Every conversion the display does
is one the person
doesn't have to.
Ask your agent: give me the answer, not the parts
Agents often return raw figures and leave the last step to you. This prompt asks for the last step:
I'm going to use your answer to make this decision: [describe the decision]. Don't give me raw figures to work out myself. Convert everything into the units I'll use, compare it against my limit or target, and say the result first: "over by X," "under by X," or "reaches X in Y." Show the calculation after the answer, in one or two lines, so I can check it. Data: [paste here]
What good output looks like: the first line is the answer to your decision. The math comes after it, short enough to check.
Sources
- Christopher D. Wickens, John D. Lee, Yili Liu and Sallie Gordon-Becker, An Introduction to Human Factors Engineering, 2nd edition, 2004. Includes the principles of display design, such as predictive aiding and reducing the cost of finding information.
- The speeds are example numbers. The trend arrow is shown generically, not as one aircraft maker's design.