For the Heart Rate, non-standard ways of wearing your watch can affect the accuracy of the heart rate monitor, meaning that the green light may not be fully covering your skin because of the arm swinging, slight movements, or even because of the sweat.
It may also cause inaccuracy because of the smartwatch being too tight, or your skin having tattoos, hairs or scars.
When measuring your heart rate, please remember to keep your arm flat and keep the sensors clean of dirt and sweat.