Abstract: A method for operating a fluid meter, in particular a clamp-on fluid meter, in which a first measuring arrangement is arranged on a fluid-conducting pipe. Fluid flow quantity determination is carried out with the first measuring arrangement. A second measuring arrangement includes an ultrasound transducer that emits an ultrasound signal along a second measurement path. The signal is reflected at the pipe in the direction of the ultrasound transducer. The second measurement path is substantially orthogonal to the pipe and/or flow direction of the fluid. The time of flight of the ultrasound signal along the second measurement path is determined and changes in the flow cross section are found based on the time of flight of the ultrasound signal along the second measurement path. A correction of the first measuring arrangement is carried out with the aid of the changes in the flow cross section.