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I have to display some information about a battery system on a very limited display. It only has a four characters dot lcd display space, so the most common thing I saw for this was alternating the information. The information needed to be displayed is voltage, load state and for some cases temperature. So I to display for example:

  • 37.5
  • 098%

(yeah, no V for voltage available) and for another case of a similar device, it would additionally display

  • 37°C

So I was experimenting with different display durations. I first tried 500ms which for me works fine, but looks a bit hectic. Also this has to be usable in not-so-optimal light conditions and I am afraid that people will have problems reading it there. I started not looking "hectic" to me at ~1500ms but then I have the feeling that I need to wait for being able to read the information, and quickly accessing the information is important too.

So I am not only looking for the answer of "hey, use 666ms, its cool" but also for a good explanation at how to arrive at the number to be able to reason about it for the next time ( where I might need 4 or 10 informations )

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2 Answers 2

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One solution is to provide two modes to build flexible system:

  1. Scan mode auto-scans the subset of most important params (gray-filled) with delay of 1s.

  2. Manual mode is activated with additional key. Then displayed params are switched manually, by each key press. If no action is performed for 4s, then device automatically switches to Scan mode again.

enter image description here

Pros:

  1. Both time settings are enough to notice current param.
  2. Scan mode provides fast looping through subset of important params, so even if they miss the needed param, it will be shown again quite soon.
  3. Device works with minimal key pressings

Con: users should have appropriate mental model, as modes add some complexity to the system

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  • Nice, although I will have to evaluate if we can add a button. Maybe I can repurpose the lcds shielding as a button, even with gloves only about half of it would be covered when pressing. For the transition from scan to manual, would you give any recommendation on if the first manual should always show the same thing, or if it should be a "fast forward" of the current scan mode state? Commented Sep 29, 2014 at 12:03
  • LCD sheilding as a button has poor affordance. Separate key is much better. Also while pressing on the screen, they hide current value with fingers. So it's not good idea. Commented Sep 29, 2014 at 12:20
  • First manual could be either next param, or first param from secondary set. It's more to the interaction style and context. Commented Sep 29, 2014 at 12:23
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In "Design with the mind in mind", author Jeff Johnson dedicates chapter 14 ("We have time requirements") to the "durations of perceptual and cognitive processes, and based on those, provides real-time deadlines that interactive systems must meet to synchronize well with human users" in order to be effective and perceived as responsive.

In the chapter you can find a detailed table with processes and their duration.
In this case, I think you might be interested in considering the length of the following processes:

  • Time lag between a visual event and our full perception of it (or perceptual cycle time): 100 milliseconds (0.1 second)
  • Time for a skilled reader's brain to comprehend a printed word: 150 milliseconds (0.15 second) (important: in this case it's not a printed page)
  • Time to identify (i.e., name) a visually presented object: 250 milliseconds (0.25 second)
  • "Attentional blink" (inattentiveness to other objects following the recognition of an object): 500 milliseconds (0.5 second)
  • Duration of saccade (involutary eye movement), during which vision is suppressed: 100 milliseconds (0.1 second)

According to the list above your minimum display duration is about 1 second. But in this case we assume the users are a) quite skilled and b) already 100% focused on the display (which I'm not sure is your case).

In particular, I guess we have at least 2 main additional variables to consider:

  1. Context of use (day/night, light level, busy/quiet environment, distraction factors, etc.)
  2. Users (perceptual and cognitive processes can take longer in older users or be faster in other users - e.g., Vipassana meditation seems likely to reduce Attentional Blink)

Considering a) human perceptual and cognitive deadlines and b) testing the interval on your users I'm sure you'll come up with the best compromise for duration.

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