The register accuracy can be easily explained by means of four-color printing: In order to obtain a print image in four-color printing, a sheet of paper runs through several successive inking units, with one color being applied to the sheet for each inking unit (in four-color printing, cyan, magenta, yellow and black). The colors are printed step by step directly on top of each other and thus result in the finished print image.

In order to obtain an exact print image, the register in the printing machine is aligned for this. This is done optically using fiducials or using digital web monitoring. The register accuracy, also known as register fluctuation, describes the resulting offset of the superimposed colors during printing. In order to keep the register accuracy as high as possible, the printing press requires the highest level of precision. This is the only way to achieve the best possible accuracy of fit of the individual color prints for a sharp print image. If the offset of the color separations is too great, the print image appears blurred and readjustment must be made.

Depending on the printing process (with the exception of digital printing), register fluctuations cannot be avoided as these are caused by the machine. With a high level of register accuracy, these can be kept very low (they are, for example, +/- 0.15 millimeters) so that they do not affect the quality of a print image.