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I recently criticized a sketch of a automobile instrument cluster concept that indicated speed with a bar gauge and a numeric readout. I and many others suggested that a dial speedometer was easier to read at a glance or peripherially. Then we were challenged, asked "is this an assumption or is there research to support that claim?"

I thought surely there is plenty of research on this topic but I couldn't find any! Does anyone know of any research comparing the effectiveness of various formats of speedometer (dial, numeric, bar)?

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  • 1
    Here is an interesting text on speedometer design and why it works better compared to just a numeric screen: blog.visual.ly/speedometer-design-why-it-works
    – Samuel M
    Mar 10 '15 at 16:59
  • And since my 5 minute edit time just went past on the previous comment, here's another document (36 page pdf) about the development of speedometer dials (has some of the same points noted about dial speedometers giving more information than just one exact number representing the speed): epublications.bond.edu.au/cgi/…
    – Samuel M
    Mar 10 '15 at 17:08
  • @SamuelM - much appreciated.
    – obelia
    Mar 10 '15 at 17:34
  • The dial is a great design for many reasons - many of the right reasons. Digital displays are vastly superior to anything physical so whatever you do has that advantage. But simple numbers or a loader bar are bad designs. Recreating a physical gauge is still the design to beat. I think we will have numbers and bars in the HUD and an lcd dash that unboxes looking like dials but can end up being whatever. You can see speed in hud and have maps, phone and music center dash. The extra display could be controls since you cant reach the dash display.
    – moot
    Mar 10 '15 at 17:46
  • @Samuel M: That link has a lot of good points about why a dial speedometer works for many purposes. The problem is that few if any of those are things I (or I think most competent drivers) actually want from a speedometer. I don't, for instance, look at the speedometer to see how fast I'm accelerating, or whether I'm at an appropriate speed to merge with traffic. I look at a speedometer basically for one reason: to see whether I'm exceeding a posted speed limit, and for that I think a digital readout is best since it allows direct comparison with the sign.
    – jamesqf
    Mar 10 '15 at 19:51
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There is a lot of research on this topic.

1. Overview

Here's an excellent review from the University of Michigan Transportation Research Institute on the performance of different gauge designs, including linear, radial, and others:

http://deepblue.lib.umich.edu/bitstream/handle/2027.42/793/78868.0001.001.pdf?sequence=2

It covers a broad range of gauge designs, and answers very interesting questions on reaction time, performance, calibration, orientation, etc. The report is a bit dated, but since the performance of gauges is largely driven by physiological visual perception, the relevance has barely changed.

The research shows, not surprisingly, that analog needle dials perform better than linear meters.

2. Additional observations

Some additional considerations that are not covered by the report:

  • Visual focus for humans is circular, not linear. So for quick glances, radial dials place more information closer to the point of focus for the eye.

  • We are more visually sensitive to rotation than to horizontal length. It's easier to perceive a change in angle than a change in horizontal length. It's an evolutionary thing. So changes in radial dial rotation are more perceptible than changes in horizontal meter length.

  • Horizontal speedometers present a layout issue which is a real problem. The temptation will be to place additional information above or below the speedometer because of space constraints. That creates all kinds of problems with distraction and orientation for quick glances. One of the nice things about dials is, they can occupy the center of a dashboard and remain relatively free of distractions.

3. Digits suck

There are a lot of issues with digit readouts. This report studies relative performance and you should find more citations stemming from it. The one case where I've seen digital readouts work reasonably ergonomically is in heads up displays in cars. Otherwise, they tend to be just helpful secondary indicators for additional precision (e.g. when setting cruise control speed), where a dial is a better primary indicator.

4. More research

For more research, here is a category listing on speedometers from the Transportation Research Board:

http://trid.trb.org/results.aspx?q=&datein=all&index=%22Speedometers%22#

That should provide you with an excellent springboard to follow citations/references to accumulate a lots of research quickly.

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  • Thanks tohster. That U. Michigan link you posted is the most informative thing I've found so far. Thanks. The fact that's it's a scanned document probably means it wasn't indexed by google and explains why it wasn't found by my searches.
    – obelia
    Mar 11 '15 at 20:43
  • @obelia I think if you follow some of the citations you will quickly build a good library of research.... I was too lazy to pull on the thread myself :-)
    – tohster
    Mar 11 '15 at 20:51
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In a report and ebook published by ustwo, the authors argue that traditional dial-based instrument clusters are feature-rich but context-poor in that all information is displayed at all times. For example, the speed and rev dials are displayed even when the car is stationary. Instead, they propose that showing only the most appropriate information to a driver according to context can be easier to interpret at a glance and reduce distraction.

The early speedometers worked directly from the engine: a cable connecting the two pulled the pin left or right depending on the exertion put upon the engine. Though these mechanics are no longer used, the same method to communicate velocity is still adopted in nearly all cars. Is a dial pointing at a number really the most effective way of communicating a driving speed?

There is an argument that it signifies a relative position — akin to ‘How many minutes to 2 o’clock?’ as seen with traditional watch-faces. But there are new and more relevant measures for speedometers now, such as ‘How close you are to the speed limit?’ So, it is, in a way, a legacy; the familiar representation carried over from a time when that method was the best approach within technological and mechanical constraints.

So they are making the point that dials are great a displaying information relative to a fixed context, whereas modern technology allows us to present information in a dynamic context. For example, we could show current speed speed in relation to the local speed limit or other parameters such as weather, or combine the fuel gauge and range so that they are shown both as absolutes and in relation to the journey.

Circular dials aren't necessarily the best way to represent this type of contextual feedback.

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  • I was actually discussing the issue with one of the authors of the ustwo article and that led me to post my question here. One of my points in that discussion is that they hadn't performed/consulted enough research to make to make some of the assumptions they were making.
    – obelia
    Mar 11 '15 at 20:41
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This all boils down to what information an indicator needs to convey and how practical it is to make one that conveys it.

In the old mechanical days, it was always more practical to make the dial-type for everything (clocks, voltmeters, speedometers etc.) In the digital world, it's more practical to make them solid-state numeric.

Do we still need dials? In some cases (e.g. anything with a non-linear scale, like an ohmmeter) yes. If we need to be able to place a value on a scale and it is more important to know where on the scale it fits rather than what the exact value is, like an RPM meter again, yes.

What do we need from the speedometer mostly? To not pay speeding tickets. Period. Precision here is key, not where we are on the scale; in the rare cases that we do need that, we can visualize that internally pretty well anyway. Honda understood this as well. Other makers have the digital option in the modern digital dashboard, but not as big as Honda.

So, for speedometers, numeric is the way. (For RPMs, temperature, fuel etc. keep it as a dial or a bar graph.)

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