1. A device for determining a coarse component of a position datum of a moving craft, said position datum representing one of a latitude of the moving craft or a longitude of the moving craft, said position datum being reconstructed cyclically in accordance with cycles of reconstruction of the position datum, by combining said coarse component acquired cyclically in accordance with cycles of acquisition of the coarse component, with a corresponding fine component acquired cyclically in accordance with cycles of acquisition of the fine component, comprising: an acquisition module configured to acquire said fine component in accordance with cycles of acquisition of the fine component and to acquire the coarse component in accordance with cycles of acquisition of the coarse component, wherein the cycles of acquisition of the fine component are executed at a first frequency, and wherein the cycles of acquisition of the coarse component are executed at a second frequency lower than the first frequency; a first determination module configured to determine a sign of a difference between the fine component for a given one of the cycles of acquisition of the fine component and the fine component for the preceding one of the cycles of acquisition of the fine component; a second determination module configured to determine a sign and a value of the speed of the moving craft based on speed data from a computation system; a computer configured to compute the coarse component corresponding to said given one of the cycles of acquisition of the fine component, as a function of said sign of the difference between the fine component for said given one of the cycles of acquisition of the fine component and the fine component for said preceding one of the cycles of acquisition of the fine component, and as a function of said sign and said value of the speed of the moving craft.