In the past, without close physical references, it was difficult to measure the speed at sea. The process began with the release of a trunk or a piece of wood that had a rope tied from the ship’s stern. They would float over the surface of the water and wait for the trunk to stop, and then they would measure the speed at which the boat would move away from the wood.

To calculate the distance, knots were made at the rope, with approximately 47-foot wide intervals, and the knots were counted as the rope was leaving the boat.

However, to measure speed, in addition to the distance units, time units were needed, and to do so, sandpieces of about half a minute were used. Therefore, in this work, two people were needed: one to flip the clock and the other to count the knots. And because the tools used were not very precise, the results were mediocre.

However, the ratio between time and knots was adjusted until coinciding with the nautical miles of that time, and nowadays, at the time of the satellites, there are still nodes the units used to measure the speed at sea.