Hi. Heart rate or pulse rate is a dynamic vital parameter which varies with your movement, emotion, physical activity and in young people even with normal breathing.
heart rate tends to increase with inhalation and decrease with exhalation in normal healthy young people.
The graph you shared shows that your heart rate has remained between 60-75bpm in the 30s time period. Which is ok. It's not off the mark.
Whenever you took a breath the RR decreased your heart rate increased and whenever you exhaled your RR increased heart rate decreases. Add to that movement and state of mind.
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It is best to not overanalyse these parameters even though easily available in multiple devices and smart watches now a days as it can lead to confusion and anxiety.
Artifical intelligence and devices are definitely helpful but have the limitation of calibration, possible artefacts etc
If you have any symptoms or any background risk factors or family history to suggest any kind of precaution, it's better to consukt a doctor.