I did some research before I implemented this feature. There's a bunch of different sets of tresholds (some say "normal" is below 110, some say below 130...). Wikipedia ( http://en.wikipedia.org/wiki/Blood_pressure#Classification ) says 120 and 80 are still in the normal range. I based bp chart's settings on "The Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure" ( http://www.nhlbi.nih.gov/guidelines/hypertension/jnc7full.pdf , page 9), because it seemed to be the most competent source.