Carbon copying, often abbreviate to c.c., is the technique of using carbon paper to produce one or more copies simultaneously during the creation of paper documents. A sheet of carbon paper is sandwiched between two sheets of paper and the pressure applied by the writing implement (pen, pencil, typewriter or computer printer) to the top sheet causes pigment from the carbon paper to make a similar mark on the copy. More than one copy can be made by stacking several sheets with carbon paper between each pair. Four or five copies is a practical limit. The top sheet is the original and each of the additional sheets is called a carbon copy. Care must be taken to ensure that each sheet of carbon paper has the carbon side down.