El Primero is a high-frequency chronograph movement developed by the Swiss watchmaker Zenith in 1969. It was one of the first automatic chronograph movements and is known for its precision and reliability. The movement operates at a frequency of 36,000 vibrations per hour, allowing it to measure time to 1/10th of a second. The El Primero movement has been used in various luxury watches and is celebrated for its engineering excellence. Its design has influenced many other watchmakers and remains a significant achievement in horology, showcasing the innovation of the late 20th century.