Blood Pressure is charted against Heart Rate to provide correlational data about your cardiovascular health. (1)
Blood pressure data is graphed for matching biometric paired entries in the diary: a systolic and diastolic entry.
Entries are paired in the order they appear in the diary, or if they have timestamps then the closest timestamped entry within 10 minutes.
After a blood pressure pair is found, if there are pulse entries for that day, they are also graphed, with the same rules (if they have time within 10 minutes, otherwise by order).