A device measures at least a first physical quantity of fluid flow in a three-dimensional space having at least one predetermined interface, between at least two media. The device comprises a computer prescribing first and second conditions at the different boundaries concerning the first physical quantity, associated respectively with a first source and a second source, different to one another, the first and second sources being point sources of mass flow of fluid and/or of force. The computer calculates, by distributed point source calculation, a first value of the first physical quantity from the first condition and from the first source and a second value of the first physical quantity from the second condition and from the second source, at at least one second point, different from the first test point, then combines the values to calculate for the first physical quantity respectively from the different boundary conditions and sources.