On this day 165 years ago, on May 21, 1860 (April 1, 1860 lunar calendar), the inventor of the electrocardiograph machine, William Eintofen (1860-1927) was born. Eintofen (1860-1927) Dutch physiologist. Born in Java on May 21, 1860, and died in Leiden on September 28, 1927. His father was a military doctor stationed in Java. He entered the Medical School of Utrecht University in 1879. He received his medical degree in 1885. The following year, he served as a professor of physiology at Leiden University and later became a member of the Royal Netherlands Academy of Sciences. In 1895, based on the work of the British physiologist A.D. Waller, he began to study the current of cardiac action. He improved de Ascenwa's mirror galvanometer and designed a string galvanometer. The silver-plated quartz wire with a diameter of 0.002 mm was used instead of the moving coil and mirror to record the cardiac current and heart sound, overcoming the shortcomings of previous instruments. In 1903, he determined the standard unit of measurement for the electrocardiogram, that is, the shadow line recorded by tracing fluctuates by 1 cm on the ordinate, representing a potential difference of 1 millivolt, and the movement of 1 cm on the abscissa is 0.4 seconds. The waves on the electrocardiogram are marked with letters such as P, Q, R, S, and T, and the electrode plates are placed with both hands and left feet to form three standard leads (still used today). In 1912, he studied the variation range of the normal electrocardiogram and proposed the "Eintofen Triangle" theory. For his research on the mechanism of electrocardiogram and the invention of the electrocardiogram tracer, he won the Nobel Prize in Physiology or Medicine in 1924. Representative works include "Color Difference Solid Mirror", "String Current Meter and Measurement of Cardiac Action Current".