Offset is the most common printing method for cartonboard. The most frequently used method is sheet-fed offset, in which the printing press is fed with cartonboard sheets. This contrasts to web offset, which is reel fed. Offset is an indirect printing method, that is, the ink is not transferred to the cartonboard sheet directly from the printing plate. The printing cylinder sets off (hence “offset”) the printing ink onto a rubber-covered blanket cylinder, which transfers the ink/printing image to the cartonboard sheet. “Offset” usually refers to offset lithography, a printing method in which the image areas to be printed are distinguished from the nonimage areas by the use of chemical properties rather than differences in level.