The flexographic industry makes use of determined angles to print CMYK colors. If a pattern is not set up according to the standard angles, moire occurs. This is referred to as an interference pattern caused by the out of register overlap of two or more regular patterns such as dots or lines. In flexographic printing, it can be caused by incorrect relative screen of the anilox rolls and halftone plate. Screen angles are selected to minimize this pattern (source: The Essential Handbook for Flexography & Packaging Printing).