Hypertension, or high blood pressure—also known as the "silent killer"—affects more than 60 million Americans. Blood pressure measuring devises are the only means through which high blood pressure can be detected. In the course of his pioneering work on blood circulation in the 1600s, William Harvey (1578-1657) noted that blood pulsated out of a severed artery as if it were under rhythmic pressure. Nearly a century later, Stephen Hales (1677-1761), an English clergyman and physiologist, devised a technique to measure the pressure exerted on the vessels as blood was pumped through them. Hales inserted a brass pipe into an animal's blood vessel and used the windpipe of a goose (for its flexibility) to connect the pipe to a long glass tube. The height to which the animal's blood spurted up into the tube gave a measure of the force...