According to the national Centers for Disease Control and Prevention, programs promoting step goals--such as walking 10,000 steps per day--can encourage people to exercise enough to reap health benefits.

The aim, the CDC says, is 30 minutes of moderate exercise, five or more days a week. All steps count, whether up a mountain or around town, as long as they’re brisk enough to boost your heart rate and you walk for 10 minutes or more.

A pedometer keeps track of steps for you. It also can be a good motivator, found a study released in June 2004 by the American College of Sports Medicine. Participants who used pedometers added about 2,000 steps per person per day to their routine.

All this makes the pedometer sound like a great gadget. Too bad that many are inaccurate at the slow speed favored by people beginning to walk for exercise.

We tested 12 basic pedometers (they count steps) ranging in price from $12 to $55 and 3 speed-and-distance monitors (they track pace) that cost from $100 to $200. We asked eight volunteers to wear pedometers while walking on a treadmill at 2.5 mph (equivalent to a 24-minute mile) and 3.5 mph (a 17-minute mile) and compared the devices’ step counts with actual counts. We also assessed durability with an apparatus that cycles up and down to simulate walking. To test speed-and-distance monitors, we checked distance readings after walkers completed a measured course. (If distance is accurate, speed will be, too.) And we looked into the features you’ll need in a walking shoe (see our October 2004 report, Walking shoes: Fit and features).

Only three basic pedometers were accurate within 5 percent at 2.5 mph, and only one of the speed-and-distance monitors provided the accurate distance within 5 percent. Most of the other devices were off by 5 to 10 percent, and a few pedometers were off by 20 percent or more. The worst were so inaccurate that if you walked five miles, they might say you’d covered three to seven.

At 3.5 mph, the pedometers did far better: All but one were accurate to within 5 percent. They also proved durable. All were still counting after the equivalent of 500,000 steps, or about 250 miles.