Stories We Like: A Guide to the Comma
a device for making duplicate copies from a master copy of printed, typed, drawn, or other material and utilizing various reproduction techniques to this end. The major types of duplicating machines are stencil (or mimeograph), hectograph, multilith (or offset lithograph), and imprinting (qq.v.). Regardless of the process used, all duplicating machines require the preparation of a master copy from which copies are made by a machine. Duplicating machines are thus differentiated from copying machines, in which copies are made from an original in an exposure-image-forming process.