Abstract: To achieve accuracies of the order of 0.75% of the measured value, a digitized, two-dimensional overall image of a bluff body (7), of the internal surface of a measuring tube (2) in the area of the bluff body, of the two fixing zones (71, 72) of the bluff body, and of contour line (51) of the inlet end (5) of the measuring tube is generated by a high-resolution electronic camera (9) located in front of the measuring tube (2) on the axis (3) of this tube. The overall image is divided into three partial images. The first partial image contains only information about the inlet end (5) and the internal surface (4) of the measuring tube, the second contains only information about the bluff body (7) without the fixing zones (71, 72), and the third contains only information about the fixing zones. From shape information about the fixing zones (71, 72) and ideal information characteristic of the ideal shapes of the fixing zones, cross-correlation information is formed.