The published standard for taking blood pressure is for the arm to be elevated so that the elbow is level with the heart. My job requires that I take a physical every 2 years. In Minnesota where I live, all but one of the clinics I've visited take blood pressure with the arm straight down at the side. I've tried it both ways at home. I see an increase in 15 - 20 mm HG with the arm hanging down. If this is typical, then in order to reach the target rate of 120/70, one would have to have a real blood pressure of 100/50.