Qualitative or quantitative: some thoughts on automobile fuel gauge design

The absolute best user interface idea ever in a car is that little arrow next to the fuel pump icon on the fuel gauge, you know the one I mean. (And if you’ve never noticed this before, you’re welcome :)

Maybe not absolutely necessary after you’ve had your car for a while, but very (very) useful when driving an unfamiliar car, like a rental. Other than that, I have to admit never really paying much attention to the fuel gauge in a car (at least not until the low fuel light starts blinking!). Not until I found myself in one of those aforementioned rental cars, anyway.

In my experience the fuel gauge in most vehicles, such as my Nissan Frontier, is based on textual indicators, specifically Full and Empty.

Fuel gauge in a Nissan Frontier

On the other hand, the VW Passat I once rented had a a gauge based on numerical indicators, with a full tank represented by 1 and an empty tank interestingly not indicated by either text or number.

Fuel gauge in VW Passat
Fuel Gauge in VW Passat

Having the fuel gauge top out at 1, with the halfway point being 1/2 and empty (presumably) 0, is somewhat reasonable in a mathematical sense. And interestingly, the value of “half” works in either/both the textual and numerical senses.

But most people aren’t really interested in the math of the situation, they’re not thinking, “Oh, I’m almost at zero fuel.” They’re thinking (as the low fuel light blinks at them), “Oh, the tank is almost empty.”

I can’t help wondering how the systems engineers and the user experience team at VW decided to use to indicate a full tank. What was the decision-making process, and what were the evaluation criteria? Is this a case of engineers being engineers? Perhaps a cultural thing, something uniquely German? Or is there something else at play here?

If you know, please share.

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