Abstract: The ring-shaped sighting device comprises an annular ring-shaped space the axial height of which decreasing from a window provided in the annular space for observing the level of the liquid to the opposite side. Hence, the uneven bottom forms a displacer for the liquid present in the annular space, so that the volume of this liquid versus its surface can be maintained of a low value on the entire periphery of the annular space. In this way, thermal dilatation of the liquid has no significant importance on the level of the liquid which guarantees an indication largely independent of the temperature.