
If you get your blood pressure measured, arm position is important. As this piece states:
When the arm is on the lap or the side, a blood pressure reading can be erroneously high. But when the arm is supported and at heart height, a blood pressure reading is more likely to be right.
Whenever I go to my doctor, she makes sure my arm is in that position. When you get your blood pressure read, make sure you do so too.
Don’t just take my opinion, though: ask your health professional.