A couple of days ago I noticed that there was a sudden change in how many calories my 530 was registering, about 60% down. I figured my hrm dual had an ingress of sweat so cleaned and washed strap. I then even purchased a new one as well. So today went out and still noticed was the same so was confused by this and pulled up to check settings. Loan and behold i found that the heart rate zones and max heart rate had changed to 232, totally incorrect! I figured the hrm monitor had give a false reading, thus changing via auto detect the max heart rate. Changed it back to correct figure of 172 and calories all back to normal. Just thought i would post my fix