MODEL RELEASED. A GP measures the blood pressure of a young woman. Blood pressure is a measure of the pressure that the circulation exerts against the walls of the main arteries and is measured in millimeters of mercury (mmHg) using a sphygmanometer (shown) at the brachial artery of the arm. Two measurements are recorded, one taken when the heart is in contraction (systole) and a second during relaxation (diastole). Normal values for a young adult would be 120 mmHg for the systolic pressure and 80 mmHg for the diastolic; these are usually recorded as 120/80.