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A much faster approximation that is not too far off over the range of everyday non-extreme temperatures: C → F: times 2 then plus 30 F → C: minus 30 then divide by 2
A much faster approximation that is not too far off over the range of everyday non-extreme temperatures: C → F: times 2 then plus 30 F → C: minus 30 then divide by 2
This is what I use. I'm not quick with arithmetic in my head so if I want anything more accurate it's faster to just grab my phone.
C * 2 - C / 5 + 32, where I just round C to the nearest multiple of 5 before dividing to make it easy.
24C times 2 is 48, 24 / 5 ~= 5, so 43 + 32 = 75. Off by less than a half a degree, which (thinking about it for 15 seconds or so) I think is guaranteed under this system.
The most important thing is that this is easy to remember because it's basically just the real conversion, but also easy to do in your head.
If the "refined approximation" assumes it's easy to 1) subtract 10% 2) double and 3) add 31, then it should be just as easy to 1) double 2) subtract 10% and 3) add 32 - i.e. the exact conversion formula.
Or we can stop using freedom units and join the rest of the world. Take a small step to make this happen right now: set your phone and thermostat to show you the temperature in Celsius. I did this and my kids are growing up with an intuitive understanding of what 20 degrees C feels like.
Or we can stop using freedom units and join the rest of the world. Take a small step to make this happen right now: set your phone and thermostat to show you the temperature in Celsius. I did this and my kids are growing up with an intuitive understanding of what 20 degrees C feels like.
You got them on meters and liters as well?
Or we can stop using freedom units and join the rest of the world. Take a small step to make this happen right now: set your phone and thermostat to show you the temperature in Celsius. I did this and my kids are growing up with an intuitive understanding of what 20 degrees C feels like.
So I do not want to sell anyone on changing their view. This isn't advocacy. But just want to provide one illustration of why someone may prefer Fahrenheit.
When I travel, hotel rooms generally let me alter the temperature on digital thermostats by one degree. In the US, that's great, that's plenty of precision. In Europe, I lose fidelity and am strictly worse off.
If people like a room set at 71 degrees, they don't like 72 or 70. If they like it at 75, they aren't secretly shooting for 76.
When I'm cooking in an oven or sous vide, I often want to tweak controls very precisely in an attempt to balance the carmelization of sugars or the rendering of fats while leaving proteins or starches intact.
Room temps, weather, and cooking are the ways I mainly interact with these scales. In each of them, the precision of the base unit in F is strictly advantageous to me.
Celsius can absolutely allow greater granularity, if everyone used an extra significant digit as a rule. I blame psychology though, people and systems often just don't bother to think that way.
I wholly support the metric system to unify measurement across different scales. That's neat. But as I rarely need to talk about millidegrees or gigadegrees, it seems less relevant to me in this context.
Edit: The original comment below did not take into proper account the significance of taking the floor in the approximations, rendering it mostly useless. ---- If the "refined approximation" assumes it's easy to 1) subtract 10% 2) double and 3) add 31, then it should be just as easy to 1) double 2) subtract 10% and 3) add 32 - i.e. the exact conversion formula.
In other words, (c - c/10) * 2 + 32 = 2c - 2c/10 + 32 = 9c/5 + 32.
The only difference between the refined approximation and your approximation is 31 vs. 32 in the last step. The rationale for choosing 31 is explained in the "Analysis" section of the blog post. To summarize, when we subtract 10% in the approximation method, we do not perform an exact division. Instead, we perform a floor division (discard the fractional part) for easier mental calculation. The floor division introduces an error that lies in the interval [0, 2). If we subtract 1 from the result, then the error lies in the interval [-1, 1). Therefore, in order to prevent the magnitude of error from exceeding 1 °F, we add 31 instead of 32 in the last step.
Also, I find subtracting 10% of smaller number from itself slightly easier than doing so with a larger number. That's why the subtraction step comes before the doubling step.
