Vivosmart4 is the third generation tracker i am using from Garmin, and the most inaccurate for measuring HR. I use the device mainly to track my stress level and my exercise activities on a weekly basis. When i am doing body combat hour i select running on the tracker, just to make the HR measurements more frequent. But the device shows low level of HR, such as 100 when my heart is almost to jump out of the body. My max level is 170 but the device never even comes closer to it, it stays at the level 120, peak 130. Hence i see very low level of intensity minutes tracked. This summer we went hiking and on some day we had altitude difference of 1000 meters, and the device did not register a single minute of activity. I am seriously thinking to change to another manufacturer if i do not get help in fixing this problem with my tracker. There is not point of using a tracker that does not track 