this weekWalk This Way

November 14, 2004

Pedometers

Your mileage may vary

The inside of a pedometer

Thomas Jefferson was born in 1743 and served as the third president of the United States from 1801 to 1809. He drafted the Declaration of Independence, founded the University of Virginia, and built a famous home called Monticello. These accomplishments are all quite impressive, and every schoolchild in the United States learns them (and then promptly forgets them after their exams). What I did not know until recently, however, was that Thomas Jefferson invented macaroni and cheese. That’s right: I owe yesterday’s dinner (and my favorite dish as a kid) to Mr. Jefferson. Were he alive today, I’d vote for him on that basis alone.

But that’s not all Jefferson invented. He is also responsible for the swivel chair (a descendant of which I’m now sitting on), an improved version of the dumbwaiter, the hideaway bed, and even the machine used to make macaroni. For all his innovations, he never applied for a patent, believing that his inventions should benefit all of society and not just the inventor. (He’d fit right into the open-source movement today.) But few people realize Jefferson also invented the pedometer, the little gadget you wear on your belt to tell you how far you walked today.

Stepping Into the Future
I saw my first pedometer when I was about 10 years old, and I thought it was absolutely magical. How could this little wind-up mechanical box tell how far you walked? A few years ago I got a modern digital pedometer that tells me not only the number of steps, miles, or kilometers I’ve walked but even how many calories I burned. All this from a plastic box that can be had for less than US$10 and doesn’t even require satellite transmissions. Amazing.

Pedometers don’t truly measure the distance you walk; they simply count the number of steps you take and do a simple multiplication based on the average length of your stride. For this reason, they’re not exceptionally accurate; if your stride length varies (which is more likely if you’re running or navigating uneven terrain), a pedometer may have a margin of error greater than 10%. Still, the measurements pedometers provide are accurate enough for most people, and those who need to measure distances on foot with greater accuracy can always use a GPS receiver.

A Bounce in Your Step
I have always understood that there is some sort of swinging or bouncing mechanism in a pedometer that jiggles each time you take a step, thus causing a ratchet to move (in mechanical models) or incrementing a counter (in electronic ones). But I still wondered exactly how the mechanism works, so I decided to take my pedometer apart and just see for myself. Although other designs may vary, my pedometer has a horizontal arm with a hinge on one end and a magnet on the other. The arm is weighted (to give it some inertia) and held in place with a tiny spring that’s just strong enough to keep the arm centered when it’s not in motion. Move the pedometer up or down and the arm bounces the opposite direction. When it does, the magnet swings by a tiny reed switch. The magnet briefly pulls one of the two slender pieces of metal in the switch out of contact with the other, breaking the circuit, and these breaks are what the counter counts.

OK, it’s not rocket science, but I feel smarter for having understood that little piece of engineering. I still don’t know how macaroni works. I’ll tell you as soon as I figure out how to take it apart. —Joe Kissell

More Information about Pedometers…

This article was featured in Carnival of the Walkers #48.

You can learn more about pedometers from:

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You can buy pedometers from any sporting goods store, or from Amazon.com.

More on Thomas Jefferson’s inventions: