Research shows fitness trackers can be up to 32 per cent short when measuring distance
Consumer group Which? tested more than 85 trackers and smartwatches, some costing over £500

FITNESS trackers can be up to 32 per cent wrong when clocking distances, tests reveal.
That would log competitors’ 26.2 miles in today’s London Marathon as just 17.8 miles — nearly 8½ short.
One also overstated runners’ calories burned by 30 per cent.
Consumer group Which? tested more than 85 trackers and smartwatches, some costing over £500.
Worst were the £130 Garmin Forerunner 35 and £29.99 Misfit Ray, both 32 per cent short on distance.
The £279 Huawei Watch 2 Sport and £249 Apple Watch Series 1 came top, just one per cent out.
Which? said some without GPS work out distance from multiplying steps by estimated stride length.
They are less reliable as they do not let people alter stride length.
Others use a phone-style sensor.
Those with GPS did best, but even they were up to 20 per cent off kilter.
Which? checked them on tracking steps, distance, heart rate and calories used.
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It said: “Some were wildly inaccurate.
“Consistency can be as important as accuracy.
"If a tracker is accurate on just some days, you don’t know if you’re improving.”