Antide Janvier was a pioneer, renowned for his clocks with astronomical spheres. Clockmaker to the king, in 1786 he proposed the construction of a large clock indicating the times of the tides all over the world. Although the French Revolution put an end to this project, Janvier did devise this more modest-sized clock with two dials. The lower dial indicates the time, day of the month and phases of the Moon. The upper dial is more complex: its central twelve-hour dial turns in half a lunar month (14 ¾ days). The fixed outer dial indicates the approximate time of the two high tides at several ports. An elaborate mechanism enables the time of the tides to be adjusted in function of the date of the lunar calendar.