How is blood pressure measured?

Blood pressure is measured in millimeters of mercury (mm Hg), which is the standard unit of measurement used in medicine for this purpose. This measurement reflects the pressure exerted by circulating blood upon the walls of blood vessels. Specifically, it provides two readings: systolic pressure, which occurs when the heart beats and pumps blood, and diastolic pressure, which occurs when the heart is at rest between beats. The use of mm Hg dates back to the early days of medicine when mercury was used in clinical devices to measure pressure.

Other options do not accurately convey the correct method or standard for measuring blood pressure. The ratio of systolic to diastolic pressure is indeed represented in blood pressure readings, but it's the units (mm Hg) that are specifically used for quantifying this measure. Techniques like electrocardiograms do not measure blood pressure; they track the electrical activity of the heart. Finally, liters per minute is a measure of blood flow, not blood pressure.