Before the 16th and 17th centuries, navigators did not have a precise instrument capable of measuring longitude. In 1707, a British fleet sank in the fog due to miscalculation of longitude, resulting in a catastrophe of 2,000 people who lost their lives. This tragedy shocked the country. After the incident, the British Parliament offered a reward of 20,000 pounds, announcing who could invent an instrument capable of measuring longitude, with an average time error of less than 3 seconds per day. In 1735, a carpenter's son, John Harrison, made his first astronomical clock. This new instrument is also called a chronograph. It uses the clockwork as a power source and has been tested successfully at sea. The British authorities therefore awarded him £500 and encouraged him to continue researching improvements. In 1761, Harrison's fourth astronomical clock came out. It was mounted on the Royal Defence of the British Royal Ship. The ship was tested on a voyage to Jamaica and was only five seconds slower when it arrived in Jamaica six weeks later. After a few months, the ship returned to the UK, with a total error of only 1 minute 54 seconds, far exceeding the prescribed standard. In 1772, Captain James Kirk used the copied fourth astronomical clock to sail to the South Pole. This astronomical clock also performs perfectly in cold weather below zero. A year later, Harrison received the reward he deserved. Since then, the astronomical clock invented by Harrilin has been widely used on the ocean liner. Harrison's invention provides an effective and reliable instrument for countless sailors in the future.