In the 17th century, several inventors were trying to make an accurate clock for finding longitude at sea. In pursuit of a sea clock, Christiaan Huygens, a Dutch mathematician, changed timekeeping forever when he patented the first working pendulum clock in 1656 and later devised a watch regulator called a balance spring. Pendulum clocks immediately became the best timekeepers for use on land, but they didn’t work accurately on a heaving ship’s deck. Huygens worked with several Dutch clockmakers, including Johannes van Ceulen, who made this table clock around 1680. It is one of the earliest clocks with a pendulum.