new report says fitness trackers are not so accurate in measuring  amount of calories our body burns while exercising, and that this may lead people to make poor decisions about their diet.  study is from Stanford University in  USA. Researchers evaluated  accuracy of five popular trackers. These included  Apple Watch, Microsoft Band, Fitbit Surge and Samsung Gear S2.  researchers observed 60 volunteers as they walked, ran and cycled while wearing  devices. Researchers found that none of  devices had  error rate below 20 per cent. Dr Euan Ashley, co-author of  study, said: "People need to know that on energy expenditure, [ trackers] give rough estimates."
 Stanford scientists said users of fitness trackers should be cautious about using  devices to judge what they eat. Dr Ashley said: "If you go to  gym, and you think you've lost 400 calories, then you might feel you've got 400 calories to play with." This could be  problem for those who base what they eat on how many calories their fitness tracker said they burned. One CEO of  fitness tracker company suggested  researchers may not have adjusted the user settings properly.  CEO told the USA Today newspaper that  study method could have reported incorrect data, saying: "We think  excess error reported in energy expenditure is not representative in this study, due to this methodological error."