How my car wipers work

Yesterday, it actually rained! So I got to use the long-neglected windshield wipers on my Chevy Volt. They have options that include OFF, INT (intermittent), LO, and HI:

“Intermittent” is the tricky one. There are five options shown by the horizontal white bars. Do they indicate how frequently the wipes happen? Or do they indicate the delay between wipes? Effectively, in which direction does the scale increase? I can never remember this, so every time I end up trying out different settings to re-learn how to use my wipers. In this case, a bigger white bar (bottom) means more frequent wipes, which is the reverse of the order implied by “HI” being on top.

And what’s up with the exponential growth implied by the white bars? Is that real?

As Francis Bacon might have said, “When in doubt, collect data.”

I timed the delay between wipes for each of the five settings. And here’s what I found:

If we invert this to report wiping frequency in number of wipes per minute:

So, nope, the labels on the control do not reflect actual frequency. I’ve been reading Edward Tufte’s book titled The Visual Display of Quantitative Information, and this would be a perfect example of what he calls graphics without integrity. One of his principles:

“The representation of numbers should be directly proportional to the numerical quantities represented.”

Boo, Chevrolet designers! And especially for inverting the order with respect to the “LO” and “HI” markings.

5 of 5 people learned something from this entry.

  1. Jim in PA said,

    October 15, 2018 at 6:28 am

    (Learned something new!)

    Great post! I struggle with the same thing – I have to relearn how the wiper setting work every time it rains.

    The Tufte book you linked is also great. Our company president is big fan and encourages everyone to read (and re-read) it. Good visualizations are incredibly hard, but it is amazing how powerful they are when they are done well.

    Reading your last two posts back-to-back made me think of the Gettysburg Address Powerpoint from Peter Norvig. It has been around awhile, so I am sure many have seen it, but it still makes me laugh every time time I revisit it.

  2. Jonathan said,

    October 15, 2018 at 12:22 pm

    (Learned something new!)

    I wish the wipers went exponentially faster! Oh well.

  3. Lukas Mandrake said,

    October 15, 2018 at 2:19 pm

    (Learned something new!)

    As per the blinking 12:00 problem, I believe this particular example of graphics without integrity will one day be called the “cell phone bandwidth symbol issue.”

    Neat research Kiri! Are you gonna fix it with a black marker?

  4. Kiri said,

    October 16, 2018 at 9:10 pm

    (Learned something new!)

    Jim, that’s hilarious! Slide 5 is the best! :)

  5. Kiri said,

    October 16, 2018 at 9:11 pm

    (Learned something new!)

    Lukas, you’re right! I hadn’t realized that my car’s wiper-intensity label looks like a cellphone signal indicator! Great spotting!

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