A sphygmomanometer, or blood pressure cuff, renders blood pressure readings as the systolic blood pressure over the diastolic blood pressure in millimeters of mercury, according to WebMD. A gauge on the sphygmomanometer indicates both readings.
To measure blood pressure, the doctor wraps the cuff around the upper arm, inflates the cuff, and then deflates it, listening with a stethoscope to hear the heart beating, notes WebMD. The first sound heard during deflation indicates the systolic pressure, while the last sound indicates the diastolic pressure. The force of blood against the arteries when the heart beats is the systolic pressure, while the pressure in the arteries between beats is the diastolic pressure.