A kymograph is a device that gives a graphical representation of spatial position over time in which a spatial axis represents time. It basically consists of a revolving drum wrapped with a sheet of paper on which a stylus

Stylus

A stylus is a writing utensil, or a small tool for some other form of marking or shaping, for example in pottery. The word is also used for a computer accessory . It usually refers to a narrow elongated staff, similar to a modern ballpoint pen. Many styli are heavily curved to be held more easily...

 moves back and forth recording perceived changes of phenomena such as motion or pressure.

It was invented by German physiologist Carl Ludwig

Carl Ludwig

----Carl Friedrich Wilhelm Ludwig was a German physician and physiologist.In 1842 Ludwig became a professor of physiology and in 1846 of comparative anatomy...

 in the 1840s and found its first use as a means to intrusively monitor blood pressure

Blood pressure

Blood pressure is the pressure exerted by circulating blood upon the walls of blood vessels, and is one of the principal vital signs. When used without further specification, "blood pressure" usually refers to the arterial pressure of the systemic circulation. During each heartbeat, BP varies...

, and has found several applications in the field of medicine. Its primary use was to measure phenomena such as changes in muscular contractions or other physiological processes, including speech sounds. Kymographs were also used to measure atmospheric pressure, tuning fork vibrations, and the functioning of steam engines.