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Centigrade Fahrenheit

    Outside the United States with few exceptions temperature is measured in degrees Centigrade (most commonly referred to as degrees Celsius), so therefore it will usually be us (Americans) who will have to perform Centigrade Fahrenheit temperature conversion, or convert from our Fahrenheit to Centigrade so that others can understand us. A friend of mine showed me this cute trick where you can use essentially the same equation to convert in either direction, but first let’s look at how other people do Centigrade Fahrenheit conversion:
    The National Weather Service Forcast Office (Buffalo, NY) maintains a web page entitled Fahrenheit to Celsius Converter which provides a Centigrade Fahrenheit converter. Their converter uses the equations:
Celsius = 100/(212-32) * (Fahrenheit - 32 )
Fahrenheit = (212-32)/100 * Celsius + 32
    On the MathsIsFun[.com] web site the page Conversion of Temperature - Celsius to Fahrenheit expresses the same idea with:
Fahrenheit to Celsius: “Deduct 32, then multiply by 5, then divide by 9”
Celsius to Fahrenheit: “Multiply by 9, then divide by 5, then add 32”
And now for my friend’s trick: Add 40, Multiply, Subtract 40
    When you switch direction (which way you are converting) the only thing that changes is the constant number by which you multiply. For Centigrade Fahrenheit conversion the constant is 9/5 and for Fahrenheit to Centigrade conversion the constant is 5/9. This method is mathematically equivalent to the other methods, but you don't have to remember whether to add or subtract the "32" (that makes it easier for me to remember how to do it in case I don't have a computer handy). Notice that -40 degrees Fahrenheit is the same as -40 degrees Centigrade (after initially adding 40 you end up multiplying zero by the constant and then subtracting 40 to get back where you started).
    If you have a young child that is just starting to learn about numbers, the Kidknows TM Outdoor Thermometer for kids is now available on-line and at select Learning Express stores nationwide. Please click on the thermometer to visit our home page.
Centigrade Fahrenheit
Highlight one of the temperatures, enter a number and then left-mouse-click outside the text box.