Sphygmograph

The sphygmograph (/ˈsfɪɡməˌɡræf, ˌɡrɑːf/ SFIG-mə-graf) 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.