Garmin has been singled out for selling devices that have been described as “not accurate” and cannot be trusted when it comes to measuring marathon distances.

Which magazine in the UK claims that some of their devices miscalculated the distance of a marathon by as much as 17 kilometres.

Garmin’s Vivosmart 4 was named the least reliable of several devices that were tested an example given was that over the distance of 42 kilometres a person using a Garmin device would have in fact only run 36 kilometres.

The Garmin Vivosmart 4 underestimated distance covered by 41.5 per cent, and the Garmin Vivosmart HR overestimated by 30 per cent.

The research by the UK consumer watchdog comes as the UK prepares for the London Marathon this weekend.Garmin Garmin Running Devices ‘Not Accurate’ & Cannot Be Trusted Researchers Reveal

Also coming in for criticism was the Apple Watch Series 3 it reported the target of a marathon’s 42 kilometres had been hit at just 38.2 kilometres.Apple watchOS 5 Competitions screen 06042018 Garmin Running Devices ‘Not Accurate’ & Cannot Be Trusted Researchers Reveal

Runners using the Huawei Watch 2 Sport, would find themselves around 11.6 kilometres short of the finish line.Huawei Sports Garmin Running Devices ‘Not Accurate’ & Cannot Be Trusted Researchers Reveal

Which? said it carried out its analysis using a calibrated treadmill to compare the ability of different trackers to log steps taken and distance travelled.

It urged people to research any device before purchasing and warned that buying a well-known brand did not guarantee accuracy.

Natalie Hitchins, head of home products and services at the consumer watchdog, said: ‘Running a marathon is no mean feat, so runners who are putting in the months of training beforehand will want to know their fitness tracker is trustworthy, and not jeopardising their finish times.

In response to the research, Garmin claimed that the Vivosmart 4 does not use GPS and was not recommended device for marathon runners.

The Australian models sells for $199 Garmin describe it as a dedicated activity timer for walks, runs, strength training, yoga, pool swims and others.

In a statement, a Huawei spokeswoman said: ‘The test results may vary depending on testing conditions such as indoor and outdoor environments and individual runner variances.

‘With regards to running indoors, as this particular test was carried out on a treadmill, the algorithm of Huawei Watch 2 Sport calculates the user’s stride length from the acceleration sensor data while running at different speeds.

Some step trackers don’t have a built-in GPS – so will calculate distance travelled on the number of steps that have been taken.

This is based on number of steps multiplied by average stride length – which can affect accuracy.

Other watches use GPS models or connect to your smartphone to use GPS.

GPS models are more accurate.

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