X dimension of recorded spot

In fax systems, the X-dimension of recorded spot is the effective recorded spot dimension measured in the direction of the recorded line. By "effective recorded spot dimension" is meant the largest center-to-center spacing between recorded spots, which gives minimum peak-to-peak variation of density of the recorded line. "X-dimension of recorded spot" implies that the facsimile equipment response to a constant density in the object (original) is a succession of discrete recorded spots.