A blood pressure reading consists of two numbers that are written in the form of a fraction. These numbers consist of systolic pressure (the "top" number) and diastolic pressure (the "bottom" number). Systolic pressure measures the pressure inside your blood vessels at the moment your heart beats, while diastolic pressure measures the pressure in your blood vessels between heartbeats (when your heart is resting). Although a blood pressure reading of 120/80 is typically considered normal, a person's blood pressure usually fluctuates within a certain range every day. Therefore, it's best to use more than one blood pressure reading to determine your average blood pressure.
(For more information, click Blood Pressure Readings. This eMedTV article offers more detailed information on how to measure blood pressure, and provides some guidelines for determining if your blood pressure is considered normal, high, or low. You can also click any of the links in the box to the right for specific information.)