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In radiographic installations of more than one x-ray unit the need to reproduce a film technic with different units makes it necessary that they be cross-calibrated. In standard practice the establishment of a film technic requires that visual examination be made of representative films for various anatomical structures. Because of possible inconsistencies in the physical calibration factors of x-ray units, as reported in a previous paper (1), the establishment of a set of technical factors for one apparatus would not necessarily apply to a second. The process of trial and error must be repeated with each one, and this results, in addition to the time and effort required, in undesirable patient exposure. In principle, the quality of a film depends on beam energy and intensity, with all other things being constant. A knowledge of these two factors for any individual apparatus, therefore, should suffice to establish radiographic technics based on an established technic chart for another unit. A system for p...

The classical methods of scale calibration originally formulated by Hansen (1873) and developed by Perard (1917) and referred to here, after Perard, as the methods of "simple calibration" and "cross calibration", have an extensive literature (Judson 1927; Platanov 1941). The rigorous least-squares solution in the linear case is complicated, however, and the simplified method of Thiesen (1879), known as "graphical squares" or the "method of means" (Johnson 1923) has generally been used.e set of equations