The instrument used for measuring blood pressure is
electrocardiograph
X-rays
sphygmomanometer
electroencephalograph
C.
sphygmomanometer
Sphygmomanometer, commonly called blood pressure apparatus, is an instrument for measuring blood pressure.
Electrocardiograph is a machine used for electrocardiography.
X- rays are a type of radiation called electromagnetic waves.
Electroencephalograph is a machine used for electroencephalography.