Engraving of Marey's sphygmograph, 1863. The sphygmograph was a mechanical device used to measure blood pressure in the mid-19th century. It was developed in 1854 by German physiologist Karl von Vierordt (1818-1884). It is considered the first external, non-intrusive device used to estimate blood pressure. The device was a system of levers hooked to a scale-pan in which weights were placed to determine the amount of external pressure needed to stop blood flow in the radial artery. Although the instrument was cumbersome and its measurements imprecise, the basic concept of Vierordt's sphygmograph eventually led to the blood pressure cuff used today. In 1863, ?tienne-Jules Marey (1830-1904), improved the device by making it portable. Also he included a specialized instrument to be placed above the radial artery that was able to magnify pulse waves and record them on paper with an attached pen. Marey (1830-1904) was a French scientist, physiologist and pioneer of early photography.