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December 2009 Archives

December 4, 2009

How Computers Think


A good reminder of what happens when we become careless with technology. I needed to convert temperature from degrees Celsius to degrees Fahrenheit. Out comes the trusty TI-85 calculator. Bring up the conversion menu, and into the temperature subsection. I entered my conversion:

-30 C > F

and get back -86. Almost subconsciously, this answer struck me as incorrect. A sanity check with a co-worker confirmed my suspicion that it was indeed incorrect. What was going on? After pondering, I tried the conversion again in a slightly different manner:

(-30) C > F

this time getting back -22. A quick check using the conversion formula itself:

TF=95*TC+32

verified the answer:

TF=95*(-30)+32=-22

So what happened? It turns out that in the first attempt, my trusty TI was really doing this:

-1*(30 C > F)

TI should warn users about this. Maybe they do. It has been a long time since I opened that user manual. I wonder how this works on RPN-style calculators? Or if this behavior is corrected or accounted for on the newer models like the TI-86?

About December 2009

This page contains all entries posted to Digitally Mastered in December 2009. They are listed from oldest to newest.

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