It is essentially based on an unsinkable annular float that slides vertically along an AISI 316 tube, closed at the bottom, forming a true separation element between the tank and its interior, which is constantly at atmospheric pressure. A special ultra-high-flux magnet is embedded in the float and, by lowering a magnetic counterweight inside the guide tube, allows the coupling point between the two magnets to be clearly identified. The height of the liquid is read on the lubber line formed by the upper edge of the closing flange.