I keep seeing doctors and nurses making mistake after mistake in measuring blood pressure. Have come to the conclusion the best approach is both DIY and frequently.As can measuring blood pressure (when accompanied by anxiety), which in part is why I try not to measure anything I don't have to (abaddon will have me, it will be messy, it's probably better if I don't see it coming)
Errors include cuff in wrong place, or mis-oriented, arm at wrong height, patient talking, or being talked to, during measuring, always doing the same side. Often, GPs are set up so it is a pain to do the opposite arm. But they should do both arms from time to time.
Sit down somewhere quiet. Place cuff. Check position of arm. Press Go on machine. Repeat a few times.