In offset printing the colors are output on separate lithographic plates. Failing to use the correct set of angles to output every color may lead to some kind of optical noise called moiré patterns. These patterns look like some bands or waves that mostly lead to unpleasant look of the final print. There is another disadvantage associated with incorrect sets of angle values, i.e. the colors will look dimmer due to overlapping. There are many sets of screen angles such as (15° for Cyan, 75° for Magenta, 0° for Yellow and 45° for Black). The problem is that these angles can only be achieved theoretically (except for 45° angle). Other angles are output approximately, but will produce the desired effect.
While the angles depend on how many colors are used and the preference of the press operator, typical CMYK process printing uses any of the following screen angles: