BP monitoring can be very difficult….I can’t get my right arm to duplicate my left. At the doctor’s office, I sit in a straight backed chair, uncross my legs, keep the measuring device at roughly the level of my heart and refrain from talking….by the way DON’T MOVE.
If that protocol is the baseline and one expects to get a reliable reading from a person who is going about daily activities, I’ll bet getting into the FDA guidelines/expectations is a huge hurdle. You almost have to take multiple (>10) readings and do some pretty sophisticated smoothing. Erratic readings need to be dealt with…maybe an average with some indication of confidence limits.
If a person has orthostatic hypotension, the act of standing up can cause their systolic BP to drop 20mm and recover in a few seconds….big challenge.