Vessel adapted for being arranged fixedly within a fuel tank , and adapted for enclosing at least one sensor , said sensor being dedicated for measuring at least one parameter of a fuel amount situated near the sensor within the vessel, the vessel comprising: - a top surface , a bottom surface and a sidewall arranged for limiting a volume internal to the vessel ; - means for fixing the vessel within the fuel tank , with the top and bottom surfaces situated apart from each other along a gravity direction which is effective when said vessel is fixed in said fuel tank and for use conditions of the fuel tank; - means for fixing the sensor within the volume internal to the vessel , said volume being sized so as to include free space in addition to the sensor, so that the vessel has fuel capacity besides the sensor; - a set of through-holes comprising at least a first hole arranged through the top surface of the vessel , and a second hole arranged through the bottom surface of said vessel, each through-hole being adapted for fuel to flow from inside of the vessel to outside of the vessel or from outside of said vessel into said vessel, through said through-hole; and - at least one fuel inlet separate from the through-holes, and adapted for admitting fuel into the vessel when said fuel inlet is connected to a refuelling arrangement for tank refuelling, wherein the through-holes are sized so that the vessel is progressively filled with fuel currently admitted through the fuel inlet upon on-going refuelling of the tank , instead of fuel initially contained in the vessel before refuelling has started, whereby measurement results provided by the sensor during refuelling of the tank become representative of said fuel currently admitted through the fuel inlet, and so that fuel contained in the tank outside the vessel but close to said vessel and fuel contained within the vessel become identical or mixed after fuel admission has stopped through the fuel inlet , because of fuel flowing through the through-holes , whereby measurement results provided by the sensor after the refuelling of the tank has stopped become representative of said fuel contained in the tank outside the vessel but close to said vessel. - a top surface , a bottom surface and a sidewall arranged for limiting a volume internal to the vessel ; - means for fixing the vessel within the fuel tank , with the top and bottom surfaces situated apart from each other along a gravity direction which is effective when said vessel is fixed in said fuel tank and for use conditions of the fuel tank; - means for fixing the sensor within the volume internal to the vessel , said volume being sized so as to include free space in addition to the sensor, so that the vessel has fuel capacity besides the sensor; - a set of through-holes comprising at least a first hole arranged through the top surface of the vessel , and a second hole arranged through the bottom surface of said vessel, each through-hole being adapted for fuel to flow from inside of the vessel to outside of the vessel or from outside of said vessel into said vessel, through said through-hole; and - at least one fuel inlet separate from the through-holes, and adapted for admitting fuel into the vessel when said fuel inlet is connected to a refuelling arrangement for tank refuelling, <EOS>