Blood pressure is a tricky thing. Although it can be easily read by just about anyone, the process of finding ones blood pressure can be a little tricky. For those people looking to get the most precise reading possible, an invasive procedure must be put into play. This means a device must be inserted into a person and the blood pressure must be read in that way. However, the most common way to measure blood pressure is to use something called a sphygmomanometer. This is normally referred to as a blood pressure cuff, since that is exactly what it is: a pressurized cuff that is attached around a person's forearm.
The cuff is usually placed around the upper left arm of a patient, at roughly the same vertical height as the person's heart. The patient must be in an upright position for the cuff to read the blood pressure correctly, because only in this position does the blood flow through the body as it should. The cuff is then inflated until enough pressure is placed on the brachial artery there for a reading to occur. The systolic pressure is taken when the cuff begin to decrease. The doctor places a stethoscope against the elbow and listens to hear when the Korotkoff sounds begin. When they do, the systolic pressure is taken. The cuff continues to deflate until the sounds are heard no more. When this occurs, the doctor takes down the diatolic pressure.
Two types of blood pressure cuffs are in existence: digital and manual. Both of these types have their ups and downs, though most people tend to use the digital blood pressure cuffs when they are taking their blood pressure at home or in a drug store. Digital cuffs are not only easier to use, they are also more practical in a noisy environment, since you don't have to listen for the Korotkoff sounds in order to get a blood pressure reading. These cuff types actually measure the mean arterial pulse, and then derive both the systolic and diatolic pressures from that. The only downside is that they cannot be used in certain conditions pertaining to health problems some people encounter. Manual sphygmomanometers are much more precise than digital ones, though they take more skill to operate and therefore are normally used only by doctors. They involve having to manually pump the cuff as well as listening for the Korotkoff sounds, which some people find difficult to gauge.