The Fugue

Next to a digital scale, I’d say a good probe thermometer is the most important kitchen tool that nobody has. If you’re not everybody, then you might find this reference card handy.

If you’re reading this blog, chances are you know (at least intellectually)
that the metric system is superior to the mess of a measurement system that we
use here in the US. One of the more difficult switches to make is from
temperature Fahrenheit to temperature Celsius. What do you say when people
defiantly challenge you, “ok then smartypants, how do I know what the
equivalent temperature is in Celsius?” If your experience was anything like
mine, the answer goes something like this: “Uhhhh, you subtract 32 and multiply
by nine fifths… or was that add 32, or was it five ninths… Well, you just
have to get used to it.” Or this: “It’s so superior to fahrenheit that it’s a
joke to even discuss conversions. Just remember zero is freezing, ten is cool,
twenty is nice, thirty is hot.”

Well now I have a better answer. Everyone knows that water freezes at 32°F.
Everyone knows how to divide in half and do simple subtraction in her head. So
this is how you convert from Fahrenheit to Celsius: subtract 30 and divide by
half. Let’s practice. 72°F is one of my favorite temperatures. (72-30)/2 =
21°C. The real answer is 22.22°C, but you can see we’re not far off.

The reverse is likewise simple. To go from Celsius to Fahrenheit, multiply by 2
and add 30. So 15°C becomes 15*2+30=60°F. The real answer is 59°F,
again good enough for government work.

Just how much is the error? About 5°C max for any temperature you’re likely to care about. I’ll show you: