Instruct: Classify Amazon reviews into positive or negative sentiment
Query: Difficult to use accurately

This model does not have a cheast strap. It relies on the user to constantly monitor your heart rate using the finger pads on the wrist band. This is not easy or convinient during and intense workout. To get an accurate reading you would have to be doing the same activity at the same intensity for a period of time. If you change intesity you would need to be using the fingerpads constantly.