The pressure cuff + stethoscope combo is called a sphygmomanometer. It's a pretty fascinating piece of technology: A heartbeat is only audible in the earpiece when the cuff is compressing between someone's systolic and diastolic pressure.

To use it, you get the cuff pressure high enough that you stop hearing a heartbeat in the earpiece. Start releasing pressure slowly. As it comes down, take note of where on the dial you start hearing the heartbeat. That's systolic pressure. Keep listening, and take note of where you stop hearing the heartbeat. That's diastolic pressure.

Using one feels kind of magic.