Systolic pressure refers to the pressure exerted by the blood against the arterial wall when the heart beats. Diastolic pressure is the resting pressure between beats. Mercury and aneroid meters involve the use of a stethoscope to detect the Kortkoff's sounds produced by the arterial wall in response to arterial pressure. As the cuff pressure increases, the artery is compressed and blood flow is restricted. As the cuff pressure is gradually released, blood flow is reestablished and the sounds can be heard in different phases.
Oscillometric cuffs measures blood pressure from changes in the force of the surges.
There are different types of blood pressure meters. The mercury sphygmomanometer is the most accurate and reliable type available. However, it requires good eyesight and hearing. The aneroid blood pressure meter consist of a cuff with an attached circular dial that displays the pressure readings, and also requires the use of a stethoscope. These are relatively inexpensive, but require calibration at least once a year by an expert.