Your Kalenji HBR500 has a heart rate monitor with optical reading to help you find your rhythm while jogging.To ensure an accurate measurement of your heart rate: - Wear the product with the button on the top, in the middle of your biceps- The product should be positioned in the middle of the biceps before the elbow and after the shoulder.- The product is not made to work properly on the wrist- Adjust the bracelet so that it is tight but does not interfere with your practice The product should not rotate or move on your arm.