Wearable devices monitors human activities through electronic sensors,and they are at the consumer electuonics level.It's normal for certain deviation.The user should treat data objectively. --Please do not compared to hospital equipment about reading,it is NOT a medical device ! --Before using, scan the QR code on the manual to download the app and connect it to the watch with APP. --For Android user: Please always authorize Tfit access to all phone functions and always let it operating on. and please turn on the GPS on your phone before you connect it. -- Please charge it for 2-3 hours when you receive it. it was run out of power after the long delivery. Thank you!