Blood pressure refers to the pressure measured at upper arm. It is measured on the inside of an elbow at the "brachial artery", which is the upper arm's major blood vessel that carries blood away from the heart. Blood pressure ( BP ) is the pressure exerted by circulating blood upon the walls of blood vessels. During each heartbeat, BP varies between a maximum and a minimum pressure. Gravity, valves in veins, and pumping from contraction of skeletal muscles, are some of the influences on BP at various places in the body.