This data field shows the heart rate as percent of maximum. The background color is changing depending on how much the heart rate is above a defined treshold. </p><p>To aid when doing intervals, when the heart rate has been above the defined threshold, and drops back below another defined threshold, the background color turns green to show you are recovered and ready for the next interval. Since color is a lot easier to notice than a small change in a number, the idea is that a quick glance at the watch should be enough to tell you if you are inside or outside your defined zones. </p>