A rubber cuff is wrapped around a person's upper arm and inflated. When the cuff is inflated, it compresses a large artery in the arm, momentarily stopping the flow of blood. While the person listens and watches the sphygmomanometer gauge, he or she records two measurements. Blood pressure is measured in millimeters of mercury, which is abbreviated mm Hg. The important point is that the harder it is for the blood to flow, the higher the numbers will be.
High levels are a large factor in clogging arteries.
Your blood pressure is also checked each time you donate.