It's pretty good, about +/- 5 mmHg. At worst it can bump you up/down a category- drinking a couple glasses of water can do that too, and the medical treatment

It's pretty good, about +/- 5 mmHg. At worst it can bump you up/down a category- drinking a couple glasses of water can do that too, and the medical treatment would not be any different. The electric cuff machines can be over twice as variable- about 1/20 person-measurements will read off by >20 mmHg, which is a hugely important difference.