oC to oF: conversion - ehMac.ca
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Old Mar 4th, 2003, 12:04 PM   #1
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Old Mar 4th, 2003, 12:18 PM   #2
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Google sees all. Google knows all.

temperatureF = temperatureC * 1.8 + 32

Converting fahrenheit to celsius is left as an exercise to the reader.
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Old Mar 4th, 2003, 12:36 PM   #3
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Old Mar 4th, 2003, 05:33 PM   #4
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F to C has a 9:5 relationship (so C to F is 5:9). You first have to add or subtract 32 to compensate for the different way they mark the freezing point of water.

So, example:
32F:
{ (32-32) x5 } divided by 9
{ 0 x 5 } / 9
O/9
= 0 C

100F:
{ (100-32) x5 } divided by 9
{ 68 x 5 } /9
340/9
= 37.8 C

JF's example is more elegant, but might be harder to do in your head.

Me, I just add/subtract 30 and then double C or halve F. It's close enough. (100 minus 30 is 70, divide by 2 is 35).

If you think about it, a celsius degree is "bigger" than a farenheit degree. There are 40 C steps from freezing point of water to minus 40, while F has 72 steps.

So -35F is colder than -35C. Where it gets a little strange is below -40, where -45C is colder than -45F.

Since Enviournment Canada changed the windchill rating last year, we now get windchill in numbers related to the temperature scale, not rate of calorie loss. Even though the rating is dependant on the temperature scale used (F or C) it's not correct to label it with the scale used. (What?)

What all that gobbleygook means is if the air temp is (for example) -20 C and it's windy, you're supposed to say the windchill rating is -30 (not -30 C, or -30 degrees, or -30 celsius. Just -30).

It also drives me crazy to hear the (usually) radio DJ say something like "with the windchill, it feels like minus 30".
No, it doesn't. It feels like -20 with a wind.
Some of us ehMac'ers have been outside when it's -45 C or colder. Trust me, that doesn't feel like any day with a -30 C air temp and a -45 windchill. It's feels a lot worse, and you can't make it any better by ducking behind a building.
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Old Mar 4th, 2003, 06:31 PM   #5
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At -40 degrees, who cares gives a F/C/K which scale it is? [img]smile.gif[/img] Me, I use K. Absolute. No degrees here. We're basking at 275K right now.
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Old Mar 4th, 2003, 06:36 PM   #6
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used to be jwoodget wrote
At -40 degrees, who cares gives a F/C/K which scale it is? [img]smile.gif[/img] Me, I use K. Absolute. No degrees here. We're basking at 275K right now.

It's 275 outside right now? Aieee! I'm melting. MELTING.
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Old Mar 4th, 2003, 09:48 PM   #7
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Well 25oC is 298.15K and 0 is 273.15K...
Ah Chemistry... Add a little Cs(s) in some H2O(l) and run away fast...
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Old Mar 4th, 2003, 10:09 PM   #8
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On the conversion from F to C, I have observed that;

1.8 = 2 - 0.2 = 2 - 2 * 0.10

So what, you ask?

Well, instead of temp_F = temp_C * 1.8 + 32,
temp_F = temp_C * 2 - temp_C * 2 * 0.10 + 32

Now it looks messy until you break it down.

temp_F = 2*temp_C - 10% of 2*temp_C + 32

Since multiplying by 2 and dividing by 10 is very easy (1/10 = .10) this gives us a very simple, yet accurate way to convert C to F. And can therefore be done all in one's head. Also you only need to caluclate 2*temp_C once even though it is used twice.

For example; 22C to convert to F

2 * 22 = 44
44 - 10% of 44
44 - 4.4 ( I usually round to the nearest integer)
44 - 4
40 + 32
72F ta-dah !!!!
All because back in grade 5 I learned how to factor numbers.
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Old Mar 4th, 2003, 10:19 PM   #9
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Too complicated, the world should just get on with it and standardize on Metric.

Water freezes @ 0c and boils @ 100c. There, simple ain't it?

For the life of me I can't understand why the US system is still using Imperial with their silly base 16 fractions and such. We count on base 10 so the Metris system is so much easier to comprehend.
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Old Mar 5th, 2003, 12:55 PM   #10
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" ... For the life of me I can't understand why the US system is still using Imperial with their silly base 16 fractions and such. We count on base 10 so the Metris[sic] system is so much easier to comprehend. ..."

It's called a non-tariff barrier. It raises the cost of doing business with the US for foreign firms (who have to do a bunch of conversion, revise technical docs, resubmit correct regulatory data, print new boxes, etc) while making a US exporter's costs equivalent (spends the same as a foreign firm doing conversions).

It also encourages small "cottage industries" in the US where the whole deal is just too much hassle for a potential foreign competitor that otherwise could just ship products from inventory intended for a world market.

It's not exactly a big deal, but when it comes to trade, every little bit helps and they count jobs created or lost in ones and twos, not just hundreds or thousands.

Of course for Canada, metrification allows us to export products and grow when our domestic market won't support the enterprise, so we switched for trade reasons as well.

The US is also fond of "shorting" it's measurements. That's why a US gallon is smaller than an Imperial gallon; they could charge less to gain a psychological price advantage, brag or trade based on the "bigger" capacity of it's ships and containers, etc. They made quite a buck on that one when they first adopted it, a lot of buyers were fooled for a while (and occasionally still are).

It's kind of like Microsoft creating the .WAV format when the platform-independant AIFF (Audio Interchange File Format, and no, it's not an Apple format) is essentially identical, but different. Or another one is the depreciation of the Gigabyte to just a billion bytes. Make everybody else spend money or get off the playing field and lets you make your products appear more attractive at zero cost, while you just go about your business as if there was nothing wrong and it's all an innocent little detail.

Probably the worst example of "spec inflation" was during the 1970's when some companies (the Sears catalog was one of the worst offenders) used to sell junk stereos with huge "peak power ratings" that were just fudged numbers designed to fool the innocent consumer. The FTC actually passed a law on that one, but the convenient loophole is that it doesn't apply to "portable" devices. Since to make a product "portable" under FTC rules all you have to do is put a handle on it (or make it for a "portable" car), we have 36" TVs today that weigh 150 pounds but get to use fake power ratings because there's a handle moulded on top.

But, there are a lot of examples. US TV screens sized on the whole physical CRT while in Canada you can't include the part of the screen hidden by the bezel, making "our" TV's an inch smaller diagonally; or the now famous one about computer monitors where Apple sized them according to visible area for years, then finally gave up (everybody else sized them on the CRT) and then promptly got sued for it.
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