Resting heart rate is a good indicator of any abnormality either due to short-term lifestyle changes or long-term health deterioration due to disorders. Trend analysis along with baseline gives a good understanding of the same.
Heart rate out of the healthy baseline for a short time in the night will elongate the trendline. This can be because of fever, alcohol consumption, etc. On a regular basis (2+ days) this can be an indication of disease, infection, etc. A slow increment of the baseline values shows long-term slow health deterioration due to poor lifestyle, the vice versa shows baseline shifting down due to a good and balanced lifestyle.
One can select a pair of dates to access trends for resting heart rate between them, by default weekly and monthly pairs are displayed.