Instruct: Classify Amazon reviews into positive or negative sentiment
Query: Did not work

I was very disappointed by the performance of this watch and ended up returning it. The heart rate function simply would not work consistently. Most of the time, I would press the button and nothing would happen. When I did get a reading it would be wildly different than the reading on my stationary bike (which I consider to be quite accurate.) Others seemed to have similar problems with this watch and I should have heeded their advice! On a positive note, Amazon was great about letting me return it and I got a complete refund. Buy this watch with extreme caution!