Pedometers
by Chris Woodford. Last updated: February 28, 2023.
How far do you walk in a typical day? You might be surprised at the mileage you clock up pottering round the house, nipping out to the shops, and strolling to work or school. Walking is a great way to improve health and fitness; Dr Tomislav Benjak, of the Croatian National Institute of Public Health, writes that: "Walking (hiking) is an ideal mode of daily exercise... It is safe and presents a minimum risk of injuries compared to all other physical activities. Though it is an extremely effective and healthy form of exercise, the significance of walking is rarely acknowledged, making it probably the most underestimated physical activity..." One way to get yourself walking more is to use a handy little gadget called a pedometer that counts each step you make. Ever wondered how they work? Let's take a closer look!
Photo: A step in the right direction? Wearing a simple pedometer can encourage you to take more exercise. According to the American College of Sports Medicine's Guidelines for Exercise Testing and Prescription, 5400 to 7900 steps a day is a good target to aim for, though some sources suggest a higher target of 10,000 steps a day. Photo by Dennis Rogers courtesy of US Air Force and DVIDS.
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Contents
How does a pedometer work?
Suppose I give you the job of building a little gadget that will measure how far you walk in a day. Sounds like a tricky task to me. You could use something like a clickwheel (also called a trundle wheel or surveyor's wheel—a large wheel you roll over the ground that clicks each time it turns one complete circuit), but rough or muddy ground is going to cause problems and it's going to have a job measuring stairs.
Illustration: An early-18th-century illustration of a surveyor's wheel, taken from a deck of playing cards illustrating engineering equipment. Artwork from the New York Public Library Archive courtesy of Wikimedia Commons.
Okay, so let's redefine the problem by considering what walking involves. Every time you walk, your body tilts to one side and you swing a leg forward. Then your body tilts the other way and you swing the other leg forward too. Each tilt of the hips and shift of the legs is a step. Assuming each step is pretty much the same length, all we need to do is count the number of steps we make in a day, by counting the number of times our body tilts from side to side. We can then multiply the number of steps by the length of each one to figure out the overall distance walked. This is pretty much how a pedometer works.
Photo: Pedometers can measure your steps because your body swings from side to side as you walk. Each swing counts as one step. Multiplying the number of "swings" by the average length of your steps tells you how far you've gone.
Mechanical pedometers
Early pedometers were entirely mechanical and they worked a bit like pendulum clocks (the ones with a swinging bar powered by a slowly falling weight). As the pendulum rocks back and forth, a kind of see-saw lever called an escapement flicks up and down and a gear wheel inside the clock (which counts seconds) advances by one position. So a pendulum clock is really a mechanism that counts seconds. The original pedometers used a swinging pendulum to count steps and displayed the count with a pointer moving round a dial (a bit like an analog watch). You fixed them on your waist and, every time you took a step, the pendulum swung to one side then back again, causing a gear to advance one position and moving the hand around the dial.
Here's a description of a mechanical pendulum from 1871:
"The pedometer consists of a simple arrangement of weight and pendulum acting on plane toothed wheels, by which the distance walked by the wearer is accurately measured. In size and form it resembles a small watch... The figures and divisions represent one to twelve miles, divided into halves and quarters. To the invalid, lady or gentleman requiring limited walking exercise, as well as to the hearty active pedestrian, it is equally valuable and trustworthy. It may be worn suspended from the neck, or placed in a front or waistcoat pocket, being kept upright by means of the small hook. The pedometer is adjusted with perfect ease to the step of the wearer, however, long or short, and altered at pleasure to any step required."
From An Illustrated and Descriptive Catalogue of Surveying, Philosophical, Mathematical, Optical, Photographic and Standard Meteorological Instruments Manufactured by L. Casella, 1871.
Electronic pedometers
Modern pedometers work in a very similar way but are partly electronic. Open one up and you'll find a metal pendulum (a hammer with a weight on one end) wired into an electronic counting circuit by a thin spring. Normally the circuit is open and no electric current flows through it. As you take a step, the hammer swings across and touches a metal contact in the center, completing the circuit and allowing current to flow. The flow of current energizes the circuit and adds one to your step count. As you complete the step, the hammer swings back again (helped by the spring) and the circuit is broken, effectively resetting the pedometer ready for the next step. The pedometer shows a count of your steps on an LCD display; most will convert the step count to an approximate distance in miles or kilometers (or the number of calories you've burned off) at the push of a button. Note that in some pedometers, the hammer-pendulum circuit works the opposite way: it's normally closed and each step makes it open temporarily.
Artwork: In this common design of pedometer, there's an electric circuit inside (red path) that is alternately broken and completed as you make steps. When the pedometer tilts to the left, the circuit is completed and a step is counted by an electronic circuit (top left). When it tilts the other way, the circuit is broken and reset ready to count the next step. Note how the hammer becomes part of the circuit: it has an electrical contact at one end wired to the circuit by a light metal spring (zig-zag red line). Other pedometers work in different ways, but most of the cheaper ones use a moving hammer and interruptible circuit in broadly the same way.
Animation: Inside, an "electronic" pedometer turns out to be crucially mechanical: you can see the little hammer swinging back and forth, making contact as it reaches the upper position. Animation made by us with still photographs courtesy of Lenore M. Edman, www.evilmadscientist.com, published under a Creative Commons (CC BY 2.0) Licence. (You can find the originals on Flickr here and here.)
More sophisticated pedometers (including some of the really good ones made by Omron) work entirely electronically and, since they have no moving parts, tend to be longer-lasting, more reliable, and considerably more accurate. They dispense with the swinging pendulum-hammer and measure your steps with two or three accelerometers instead. These are microchips arranged at right angles that detect minute changes in force as you move your legs.
Pedometer apps
But who needs an electronic pedometer when you've got a smartphone? Most cellphones have location-tracking devices of varying precision and you'll find plenty of pedometer apps in your favorite phone-app store. Some use your phone's accelerometers. Others use GPS satellite navigation to figure out how far you've walked or run, using space satellite signals rather than plodding mechanical counting of your steps. Most use a mixture of "location services" signals to track you as you move, including GPS, Wi-Fi, and mobile network information, and infer how many steps you've taken from your changing position.
Photo: There are lots of pedometer apps for cellphones that make use of built-in accelerometers. 1) This one's called Pedometer 24/7, runs on the Apple iPhone and iPod Touch, and seems to get good ratings from its users. As you can see here, it displays steps, average speed, total distance, and calories burned. You have to key in your height and weight to start, to give it a rough idea how long your steps are, and you can fine tune the sensitivity as well. 2) Google Fit is a more sophisticated excercise tracker that can figure out how much exercise you're taking for 120 different activities, including several different types of walking. You can track your progress over time on your tablet, Android smartphone, or desktop computer, and find out how you're doing to meet the long-term fitness goals you've set. You can hook it up to all kinds of other smartphone apps, wireless wristband trackers, and so on.
How accurate is a pedometer?
Counting steps with a pedometer sounds super-scientific, but you need to remember that it's only an approximate measurement. Not all your steps will be correctly counted and some false movements (jolts in the road as you ride in a car, for example) might be counted as steps too. Don't take the count too seriously; assume that it's in error by least 10 percent (the best electronic pedometers claim 5 percent accuracy).
For a pedometer to work correctly, you need to fix it to your waist—and not put it in your pocket—because a pedometer needs to detect the side-to-side tilting motion of your body to register each step correctly. Most devices come with a belt clip, making it reasonably easy to attach them properly. Some pedometers have a screw you can turn to alter the tension of the swinging pendulum-hammer inside them so it will register your steps correctly. If you're running, you might need to adjust it slightly differently compared to walking, for example, because your steps will likely be a different length.
