Scientific American presents Math Dude by Quick & Dirty Tips. Scientific American and Quick & Dirty Tips are both Macmillan companies.

Did you know that your calculator occasionally lies to you? Okay, perhaps it's a bit melodramatic (in an anthropomorphic kind of way) to say it "lies" to you, but it certainly can mislead you. While I don't want to shatter any relationships with trusty number-crunching companions, it's a good idea to keep this in mind.

What exactly am I talking about? It has to do with something called significant figures—something your calculator has no understanding of. But the good news is that by the end of today you will! And you'll be able to use your new knowledge to make more accurate measurements and calculations.

How to Estimate Speed
Many moons ago (it was actually many trips around the Sun ago!), we talked about a handy tip that you can use to estimate how fast somebody is running. In particular, we talked about how to quickly estimate how fast an American football player is running.

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