Sphygmomanometer: An instrument for measuring blood pressure, particularly in arteries. The two types of sphygmomanometers are a mercury column and a gauge with a dial face. The sphygmomanometer in most frequent use today consists of a gauge attached to a rubber cuff which is wrapped around the upper arm and is inflated to constrict the arteries. A blood pressure reading consists of two numbers: systolic and diastolic.