This beautiful and dual-functional instrument was well known in the 16th and 17th centuries, especially among navigators, since it provides dating of the different moon phases, as well as times of the high tide and low tide.
One side of the device shows a lunar calendar that gives the lunar phase and the lunar age (days that have passed since the last new moon) for any given day of the year. It consists of a graduated scale fixed on the outer and is divided up to represent the 12 months and 365 days of the year. On the inside a rotating disc showing the lunar phases for the period of one year.
On the other side we can find an instrument that allows us to determine the time high and low tide will take place. It is composed of an outer, graduated circle divided into fixed 24 solar hours and a revolving disc graduated for lunar time (24 hours). Is fitted with an index that allows us to read the lunar age on a scale dived into 29.5 parts. At its center is window that shows the moon during its different phases.