This object is known as a Dutch seaman's tobacco box and was used as an aide-mémoire by sailors. The box is made of brass with tables inscribed on its lid and on its base. On the lid is a perpetual calendar, which allowed sailors to work out the weekday and the lunar age for any date. The table on the bottom was used in calculating a vessel’s speed. To do this, a piece of wood was thrown into the water and timed as it passed two marks on the vessel's side. The sailor then consulted the table on the box and, from the time taken in the left-hand column, read off the ship's speed from the right-hand column.

Dutch seaman’s tobacco boxes are associated with Pieter Holm (1685/86-1776), a Swedish sailor who ran a nautical school called 'Regt door Zee' in Amsterdam from about 1737, and the words 'Reght door zee' appear on this example. They were never signed, but appear to have been made in Iserlohn, Germany, from where they were shipped to Amsterdam to be sold at Holm’s nautical school. The boxes continued to be made into the 19th century, but later examples often had errors in their inscriptions. This example, for instance, has an incorrect date of 1482 under the image of Pope Gregory XIII - this should be 1582, referring to the year that the Gregorian calendar was introduced - while there are further errors in the speed table.