Why shouldn't it be? Despite what doctors think (and tell you), arterial pressure at any point in the system does not go 'up' and 'down' with the beats of your heart. The whole of the elastic cavity comprising your large arteries is at essentially steady pressure, and blood flows down the "arterial tree" because of the pressure gradient between where it's pumped in and where it runs out. The pressure at any point can be calculated by a simple formula {pressure = flow x resistance} where 'flow' is how much blood is running down that artery at that spot, and 'resistance' is the impedance to that flow presented by all the blood vessels downstream. So it's a simple fraction, -a number. But because the dimensions of your arms are never quite equal (like boobs, or eyebrows, or ears) there'll always be slightly different blood flows in left and right, and the resistance too, will always differ. So, - the number you get when you calculate the value of the fraction is seldom the same number. Well, - it can't be expected to be, really, ... can it? I mean,..-.... even doctors should be able to understand that, -shouldn't they... ? But they don't ................ 'Lord, Forgive them, -for they know not what they do..' In fact (and I've said this before on Answers) my wife was diagnosed as "Hypertensive" by one Cardiologist, and as "Hypotensive" by another in the SAME WEEK, at the SAME HOSPITAL here in Chester, all because one took the BP reading on her left arm, and the other took it on the right. And if they'd have had their way, she'd be taking pills to "lower her blood pressure" and "raise her blood pressure" simultaneously.... Isn't it odd that they (the medical profession) can't grasp that? .... God knows, they get paid enough. - Don't you find it curious? It's really so bl**dy simple.