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In all fridges that I've ever encountered which had a manual thermostat, the scale on the thermostat was a scale of "inverse temperature":

  • 1 means keep the fridge hotter
  • 5 means keep the fridge colder

The knob

Why is it like that?

Note that on the manual the producer "cheats", specifying it's a scale of power (5 => more power => colder), but of course the actual knob controls a thermostat.

(Of course, modern fridges don't have a knob any more and they just set themselves to 3-4°C.)

  • 25
    It seems logical to me. The point of a fridge is to make things colder - so you "turn it up" to make it even colder. – Tony Andrews Aug 4 '15 at 12:39
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    you're not alone. I'm always confused by fridge thermostats (embarrassed face) – Dave Haigh Aug 4 '15 at 12:55
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    Kind of the same reason that you don't turn the volume down to 1 in order to make it less quiet. – MonkeyZeus Aug 4 '15 at 18:57
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    It also correlates to energy usage. The colder it is, the more energy it uses. If a "1" setting at 4 degrees is good enough, why waste more energy and turn it up? – nightning Aug 4 '15 at 19:57
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    I think the real question here is: does it go up to eleven? – Gusdor Aug 5 '15 at 9:25
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Because crappy designers are everywhere

There is almost no excuse for this kind of ambiguous, uncommunicative control labeling when there are so many better patterns to follow with fridge thermostats.

Here are some control formats that are far more effective.

  • They communicate the polarity of coldness clearly
  • They are color-blind friendly (some use shapes and/or labelling in addition to color)
  • Most of them are language and celsius/farenheit independent, for international products
  • Most of them can be printed using just 1 color, if cost is an isssue.
  • Most of them don't rely on a thermostatic controller (i.e. no exact temperature), although for completeness I've included one example with a temperature setting and indication for recommended temperature.

alternatives

There are pros and cons to each of these alternatives, and this list is not intended to be exhaustive. But they are all better than a naked 1-to-5 rating.

Personally I would pick a numberless volume label (either top left or 2nd from bottom, left) as it is likely to be most universally communicative.

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    Bottom-left format is not international-friendly. I have no idea how cold 35F is (granted, I wouldn't know how good 1.5°C is as far a fridge temperatures are concerned, but that's a different flaw of showing actual temperatures) – 3Doubloons Aug 4 '15 at 20:01
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    @3Doubloons it's a rather pedantic point as numbers in general aren't "international friendly" in that sense (Japanese, Chinese, Arabic, etc). The point of the illustration was to show the design pattern, not the specific format of the number which in this case will need to be tailored for the region or, alternatively, replaced with one of the other non-language specific patterns. – tohster Aug 4 '15 at 20:15
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    @plainclothes for consumer products it's more important to communicate clearly than to communicate efficiently. For example, if 1-5 is faster for you but is confusing to 20% of users, it is still a bad solution. For the numeric control, better fridges have extremely dependable thermostatic controls...if the thermostat is inaccurate or drifts then it should be obvious that the designer should not use a numeric control to begin with! – tohster Aug 4 '15 at 22:34
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    No one is nitpicking: The question is about a rheostat device -- no hard numbers allowed. More importantly, your examples all work against user expectations: A refrigerator "produces coldness" so turning the dial down or moving it to the left would indicate "produce less coldness". I think it would be good fun to watch a user lab test of these designs, but I don't think it would be a success. – plainclothes Aug 5 '15 at 5:33
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    To clarify: there's no rheostat in such "old fridges", it's just a thermostat with the weird "1-5" scale mapping (inversely) somewhere between the 2-6°C range, I guess, and with no guarantees of accuracy. The engine runs always at full power until the thermostat hits and stops it. Modern fridges can tune the engine power, are automatically set to hit 3-4°C and stay there, have multiple temperature sensors inside of it, make the air flow around to keep the temperature uniform and prevent icing... they're not the case in question. :) – peppe Aug 5 '15 at 8:36
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It matches the user's mental model, which is more important than matching real-world circumstances.

Users view a refrigerator as something that "makes cold". Therefore the number 5 corresponds to "more cold" and 1 to "less cold".

The mental model of "a device that holds its interior at a constant temperature" is more complex and harder to reconcile with things like ambient temperature and what happens when you put hot food in a cold fridge.

Labeling the dial with an explicit temperature range would be possible, but users probably don't know the specific temperature they need, and manufacturers would have to make dials in both Celsius and Fahrenheit to be able to sell internationally.

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    Seems like the 'power of coldness' idea is a bit confusing for people though. Couldn't we have a blue to red scale or something instead, albeit with red being quite small? I always though that it was degrees on my old fridge...like 1-5 degree celsius – Chris Aug 4 '15 at 13:20
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    It obviously doesn't match some users' mental models. Tyranny of the majority. – Kevin Krumwiede Aug 5 '15 at 19:44
  • Comments are not for extended discussion; this conversation has been moved to chat. – Benny Skogberg Aug 6 '15 at 16:24
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    -1 This is actually not a correct answer. The thing is, it doesn't match the mental model. The mental model of a dial that affects a thermostat is = higher the number, the hotter it is. – DA01 Aug 6 '15 at 23:44
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    I turn up an air conditioner, I expect it to get colder. Same as a refrigerator. I'm afraid that different people have different models, and the manufacturer caters to whichever they perceive as most common. Nothing stopping them from making it more explicit, though. – Ask About Monica Aug 7 '15 at 19:02
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Fridge temperature thermostat dials are just the worst. I want my next fridge to have something like this:

enter image description here

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    cute, but a happy snowman would actually be too cold for the food. :) – DA01 Aug 6 '15 at 23:46
  • -1 You would need a big dial for the drawings to be clear for anyone looking at it for the first time, or someone more elderly or with poor vision. – Tim FitzGerald Aug 8 '15 at 13:19
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Tohster's answer is great. Vote for that one. But to address the 'mental model' aspect in another answer:

The reason the dial is the way it is is that it's not a thermostat. It's actually a 'power' dial ala a volume knob. This is why it's confusing. Contrary to Nathan's hypothesis, I'd argue the problem with these dials is that they don't adhere to a person's mental model.

If we're talking temperature, a user's mental model is a thermostat. Turn it higher to make your space hotter, turn it lower to make your space cooler. This is the opposite of the fridge dial.

If we're talking volume, a user's mental model is a volume dial on the radio. Turn it higher to make it louder, turn it lower to make it quieter. Again, the opposite of the fridge dial.

But there are dials where this does have a better correlation. A fan, for instance. Any fan with a dial control will match this mental model: the higher the humber, the more power (and, the cooler you'll feel).

So that's the actual problem, there is no one mental model that makes sense here. Yes, everyone has a fridge, but:

  • people rarely adjust their fridge's temperature
  • most fridges (aside from some modern ones) offer up no user feedback to tell you if you're making things warmer or colder.

So most of us have never formed a consistent mental model of how a fridge dial works like we have with plenty of other devices we use daily.

To answer the why was it designed this way? question, I can't. I don't know why. But my guess is the same as Tohester's. It wasn't designed. It was merely the decision of one person at one time that stuck it in there and the rest just followed.

Fortunately, things are getting better for us fridge owners. Many fridges today now have actual temperature controls:

enter image description here

This matches a universal mental model: higher number = higher temperature.

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