Blood pressure readings consist of two numbers, one on top of the other. One represents the systolic blood pressure (while the heart is beating), and the other represents the diastolic blood pressure (while the heart is at rest). When several blood pressure readings are taken over a few days, your average blood pressure can be determined and you can know if you're in a healthy range.
(Click Blood Pressure Readings for more detailed information on what blood pressure readings are considered too high and factors that can cause an abrupt change in blood pressure.)