Not standard way of wearing (such as display toward wrist inner side) would affect heart rate signal measuring, such as the green light not fully cover your skin, arm swing and the slight movement of smart watch fitness watch on wrist, too tight wearing, raising the arm high and clenching the first would affect blood circulation and affect the heart rate signal as well. As with all heart-rate tracking technology, whether a chest heart rate belt or a wrist-based sensor, the accuracy is affected by personal physiology, location of wear, and type of movement.