A sphygmomanometer , also known as a blood pressure meter , blood pressure monitor , or blood pressure gauge , is a device used to measure blood pressure , composed of an inflatable cuff to collapse and then release the artery under the cuff in a controlled manner,  and a mercury or mechanical manometer to measure the pressure. It is always used in conjunction with a means to determine at what pressure blood flow is just starting, and at what pressure it is unimpeded. Manual sphygmomanometers are used in conjunction with a stethoscope. A sphygmomanometer consists of an inflatable cuff, a measuring unit the mercury manometer, or aneroid gauge , and a mechanism for inflation which may be a manually operated bulb and valve or a pump operated electrically. Both manual and digital meters are currently employed, with different trade-offs in accuracy versus convenience.