The word copying denotes reproduction. The mechanical device which facilitates reproduction are called copying machines. Copies can be obtained either by manual operation or mechanical operation. The mechanical devices like typewriter, rotary machine and photostat copying machines are used to save labour and time during the course of reproduction. Among all copying machines typewriter was the oldest type of machine operated manually or electrically. Rotary machine is an automatic copying machine. This is also known as roller copier. The use of photostat copier give exact copy of the original. This is also known as Xerox copier.
Duplicating is different from copying. It is a process of getting a number of copies of a master impression- In the process of copying copies are obtained directly from the original without creating master copy. But in duplicating copies are obtained from the master. The machine which facilitates this duplicating operation is called duplicating machine. The mechanical devices used for duplicating operation are stencil duplicator, letter-printing duplicator, offset lithographic duplicating machine and Typeset duplicating machine.