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What's a pedometer used for?
A pedometer is a beeper-sized device you wear on your waist that counts the number of steps you take.
How do pedometers work?
There are two types of pedometers, spring-levered and piezoelectric. Spring-levered pedometers use a spring-suspended horizontal lever arm that moves up and down in response to the movement (vertical accelerations) of your hips as you walk or run. The movement opens and closes an electrical circuit, and as the lever arm makes contact, a step is registered. Spring-levered pedometers must be placed in a vertical plane, perpendicular to the ground, in order for them to work. They don't work if they tip forward to a horizontal plane.
Piezoelectric is a material that generates an electric charge when it is mechanically deformed. Piezoelectric pedometers use a horizontal cantilevered beam with a weight on the end that compresses a piezoelectric crystal when subjected to movement like walking (acceleration). This generates a voltage proportional to the acceleration and the voltage oscillations are used to record steps. Got that?
Pedometers work when you dance, climb stairs, or walk outdoors or on a treadmill, but they don't work if you're biking, skiing, rowing, or swimming.
Are pedometers accurate?
The accuracy of pedometers has been carefully studied because they are frequently used in studies and researchers demand to know if they are reliable and accurate. Research shows that pedometers tend to count steps more accurately at speeds greater than 3 miles per hour (mph) than at slower speeds. Accuracy can exceed 96% when speeds exceed 3 mph, whereas the accuracy drops to between 74% and 91% at speeds from 2 mph to 3 mph, and it drops even further to between 60% and 71% at speeds below 2 mph. The error has to do with the insensitivity of pedometers to detect steps when people shuffle or drag their feet at slow speeds. Detectable vertical movement of the hips is necessary for pedometers to work well.
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