How precise is your fitness band or Wi-Fi scale?

NEW YORK — Could that be right?

That was my reaction after weighing myself on a “smart” UA Scale, part of the HealthBox-connected fitness system that Under Armour recently launched in a partnership with HTC.

After all, my non-digital, non-Wi-Fi-connected bathroom scale weighed me around 2 pounds less. A third scale at my gym fell in-between.

I’d like to put all my faith in the scale that shaved off those extra pounds, but the discrepancy got me thinking about the accuracy of the data coming at us in this connected age.

And HealthBox, which besides the scale includes a fitness wristband and a chest strap heart monitor, seemed as good a place as any to start, though the issue extends well beyond Under Armour.

There are obvious differences in determining the accuracy of a scale that is meant to stay put as compared to something you’re wearing.

FITBIT REPORT

Indeed, this past summer, researchers at Iowa State University found wide discrepancies among four tested wrist bands: Fitbit Flex, Nike+ FuelBand SE, Jawbone UP 24 and Misfit Shine. Error rates ranged from 15% to 30% and the researchers determined that the bands were even less accurate when measuring certain types of activities, including strength training.

“Researchers have known it is really difficult to get accurate estimates of physical activity,” says Greg Welk, a professor of kinesiology at the university. If the researchers have trouble, what does that suggest for you or me?

Wrists-on with Fitbit's new smart watch

Just this month, in fact, Fitbit was hit by a class-action suit from consumers in California, Colorado and Wisconsin who alleged that the company’s heart rate monitors were off by a “significant margin,” particularly so “during strenuous exercise.”

Fitbit (FIT), whose stock Friday closed at $16.60, compared with a 52-week high of $51.90, is fighting back: In a statement, Fitbit maintained that “it stands behind our heart rate technology ... and plans to vigorously defend the lawsuit.”

Still, Fitbit felt compelled to add that “it is important to note that Fitbit trackers are designed to provide meaningful data to our users to help them reach their health and fitness goals, and are not intended to be scientific or medical devices."

The company did get a boost from Consumer Reports the other day, which in testing the Fitbit Surge and Fitbit Charge HR concluded that “both … passed our tests handily, accurately recording heart rates at everything from a leisurely walk up to a fast run.” The devices can measure your continuous heart rate.

Why that Fitbit might not be so good for you

UNDER ARMOUR'S HEALTHBOX

The rubberized wrist-worn activity band that comes with Under Armour's HealthBox tracks steps and sleep and can also report on your resting heart rate. By including the chest strap as part of the pricey $400 HealthBox kit, Under Armour is pushing the notion that a more precise measurement of the heart’s activity during an intense workout or zone training requires something more.

Under Armour doesn’t claim its apps and devices are any more or less accurate than others on the market, though it emphasizes its testing process. The scale, it says, is accurate to a degree of plus or minus 1%.

Under Armour, which sells all HealthBox components separately, is about to expand its fitness-oriented ecosystem further. At the end of February, the company will bring out smart $150 running shoes that can capture data without you having to schlep a phone. This spring, it will release $250 wireless JBL headphones that promise to measure your heart rate.

Under Armour and HTC team up on connected fitness

Data from these devices connect to a newly revamped UA Record app on your smartphone. You can also connect to UA Record from a host of third-party devices, a list that includes Jawbone, Withings, Fitbit, Suunto, Misfit and Polar.

MEASUREMENT STANDARDS

For its part, Apple runs a health-and-fitness lab to collect data from employees as they work out on exercise bikes, rowing machines, treadmills and the like. Employees are even monitored in temperature-controlled chambers, given heart rate changes in heat or cold. Apple applied some of what it has learned there in producing its top-selling wearable, the Apple Watch.

Iowa State’s Welk says he has been talking to advocacy groups about coming up with measurement standards. “You might tolerate a certain level of error for steps and a different level for calories and heart rate,” he says. Being off 20% on counting steps might be acceptable, not so on a heart rate measurement.

Consumers can take basic steps to help bolster the chances that the data is meaningful. Follow instructions on calibrating any devices that require you to do so. Don’t lie about your height and weight when inputting them into an app. If you do, your calorie calculations, for example, won’t be as good.

“One key that I’d like to emphasize is that self-monitoring is one of the strongest behavior-change strategies we have,” Welk says.

Email:  ebaig@usatoday.com; Follow USA TODAY Personal Tech Columnist @edbaig on Twitter