A type of offset perfecting press, used to print on both sides of a sheet of paper in one pass through the press. A convertible perfector comprises separate printing units, connected by special transfer cylinders that flip the paper over after it leaves the first impression cylinder, allowing the second side to be printed by the second impression cylinder. One advantage of this type of press is that by adjusting the transfer cylinders so that they don't flip the sheet over, it can be used as a single-side, multi-color press. A variety of color and side combinations is possible with convertible perfectors. See Perfecting Press.