A chronometer is a precise timekeeping device designed to measure time accurately, especially in navigation. It is essential for determining longitude at sea, as it allows sailors to calculate their position by comparing local time with the time at a known location. Chronometers are often highly engineered and can withstand harsh conditions, making them reliable for maritime use. The most famous chronometer was created by John Harrison in the 18th century, which revolutionized sea travel by enabling accurate navigation. Today, chronometers are also used in various fields, including science and aviation.