What is C.I. (common impression)?

C.I. is a type of printing press in which each of several printing stations (or ‘printing units’) contacts the material being printed while the material is held against a single, centrally located drum. This drum supports the printed material while the printed images are applied. Providing the support from a single, central drum minimizes the amount of movement that occurs as the material travel between stations, and so makes it easy to maintain correct registration between the colors.