Your blood pressure is a measurement of the pressure your circulating blood is putting on the walls of your arteries, and is expressed as two numbers: Your systolic pressure (the top number, so the “120" in 120/70) is the force exerted on your arteries when your heart beats, and the diastolic pressure (the bottom number) is the force exerted when your heart rests between those beats. This pressure is expressed as “mm Hg,” which stands for...