Astute reader wargut responded to yesterday’s observation about the Fahrenheit scale being affine-ish with the following incorrect assertion:

Seriously, guys, your system is bullsh~t.

It’s on.

First, the Kelvin scale is indisputably the best of {K,℉,℃} for physics. Given that ∃ a natural zero it should be reflected in the measurement system.

American exceptionalism

But Fahrenheit is the best scale for everyday use. We are not in the science lab, so all of Centigrade’s properties that are nice in chemistry class don’t matter.

Celsians brag that 0 ℃ and 100 ℃ make it easy to remember where water boils and freezes. So what? Fahrenheit makes it easy to remember the temperature of the human body and icy seawater. Or roughly the hottest day and the coldest day.


Outdoor temperatures in Indiana range from −17 ℃ on the coldest day of winter to 39 ℃ on the hottest day of summer. During the seasons I would be outdoors for more than the necessary minimum—March to November—the daily highs are between 7℃ and 29 ℃.

So most of the relevant temperature variation — the vast differences throughout all of spring, summer, and fall—are restricted to only 23 integers. (I could use decimals, if I wanted to sound like a robot.)


When I lived in ℃ places I had to pay attention to single-digit differences like 24 ℃ versus 29 ℃, wasting the first digit.

Celsius is a scale for science, not for humans.

In Fahrenheit I get the basic idea with the first digit.

  • "It’s in the thirties" = multiple layers and coat.
  • "It’s in the nineties" = T shirt weather.

In the 70’s and 80’s I want a second sig-fig but I don’t even need 10 elements of precision. Just “upper 70’s” is enough. The first ℉ digit gives you ballpark, and the second ℉ digit gives you even more precision than you need.


In a sentence: Fahrenheit uses its digits more efficiently than Centigrade. Centigrade adopts the decimal convention but then throws away 70% of the range. Fahrenheit’s gradations are so well tuned that it only requires {0,1,2,3,4,5,6,7,8,9} × {low, medium, high}, for a cognitive savings of 7 unneeded numbers in each of 9 decades.

Celsius may be better for chemistry. Fahrenheit is better for real life.

140 notes

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    So… YEAH.
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  5. clrunklock reblogged this from sherlollysmooch and added:
    Okay but what about negative temperatures? In Celsius, when someone says “minus whatever” it’s easy to understand that...
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    This. Someone else also put it this way: You can tell the difference between a few degrees in Fahrenheit, yet in Celsius...
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