The mostrarombi (or windrose marker) is a tool, still in use in the nineteenth century, also known as Renard, meaning "fox" in French.
The name, unusual in the maritime tradition, stems from the fact that in France there was a children's game, similar in appearance to the instrument, known as Le Renard et les poules.
The Mostrarombi was invented in the Middle Age, when the sailors were mostly illiterate and were therefore not able to report, on the notebook on board or on a chart, the changes of direction and speed unavoidable during shipping.
So someone invented a tool that did not require familiarity with paper and pen. It is shaped as a disc, normally wooden, on which is traced - in bright colors - a wind rose with 32 arrows, each of these bearing eight holes, corresponding to the eight half-hour shifts.
The pegs had notches, corresponding in number to different speeds in knots . So, for example, eight pegs, with ten notches each, in the first eight holes of a wind rose direction, indicated that the ship had kept that direction during four hours at a speed of ten knots.
When changing direction and speed, for example due to weather conditions, every half hour the pilot would put pegs in other arrows with appropriate markings. This way the mostrarombi kept the waterway followed, that the navigating officer then reported on the chart, to calculate the position.
Sometimes mostrarombi had pegs without speed indicating notches, and the speed was recorded on a separate board - above or below the disc of the instrument, as in the sample shown here ( International Maritime Museum in Imperia). In it there were several rows , each one corresponding to a shift, with holes corresponding to speed values: our mostrarombi contains four rows of 15 holes, allowing to record speeds of up to fifteen knots.