I bought this as an alternative to buying an expensive GPS watch thinking it would do the trick. I was wrong. I calibrated it, re-calibrated it over and over and it would never work properly. I was trying to use this device to train for a half marathon but the times were always way off not even close to the times I did. I even went as far to take it back to the running store that I bought it at and have them help me with it but they couldn't do anything with it either. In theory, I thought it was going to be a great buy but in the end (as always for me at least) I got what I paid for. I got a product that never worked properly. I took it back and saved my money and bought a GPS since I've had no problems and all of my runs are recorded correctly which is really important when training for races. I hope that whoever reads this review has a better experience with this product than I had but I would advise to save your money!