Measurement Procedure. We mount a capillary structure in front of and at some distance from the anode, the detector
system being placed at the exit from the capillary structure. It is best to employ an image detector, or x-ray visualizer, as
the detecting system to achieve quick estimation. Comparison of the dimensions of the image of the focal spot thus obtained
with the dimensions of the image of a control object or use of a calibrating visualizer allows us to determine the absolute
dimensions of the spot.