form of drawing media. When you have finished producing the drawing on CAD, you will order the computer to send the information to the plotter, which will  then  reproduce  the  drawing  from  the  computer screen.  A  line-type  digital  plotter  is  an  electro- mechanical  graphics  output  device  capable  of  two- dimensional  movement  between  a  pen  and  drawing media. Because of the digital movement, a plotter is considered a vector device. You will usually use ink pens in the plotter to produce  a  permanent  copy  of  a  drawing.  Some common types are wet ink, felt tip, or liquid ball, and they may be single or multiple colors. These pens will draw on various types of media such as vellum and Mylar.  The  drawings  are  high  quality,  uniform, precise, and expensive. There are faster, lower quality output  devices  such  as  the  printers  discussed  in  the next section, but most CAD drawings are produced on a plotter. The Printer A  printer  is  a  computer  output  device  that duplicates   the   screen   display   quickly   and conveniently. Speed is the primary advantage; it is much faster than plotting. You can copy complex graphic screen displays that include any combination of  graphic  and  nongraphic  (text  and  characters) symbols. The copy, however, does not approach the level of quality produced by the pen plotter. Therefore, it is used primarily to check prints rather than to make a final copy. It is, for example, very useful for a quick preview at various intermediate steps of a design project. The two types of printers in common use are dot matrix  (fig.  2-17)  and  laser  (fig.  2-18).  The  laser printer offers the better quality and is generally more expensive. COMPUTER-AIDED DESIGN/COMPUTER-AIDED MANUFACTURING 2-10 You  read  earlier  in  this  chapter  how  we  use computer technology to make blueprints. Now you’ll learn how a machinist uses computer graphics to lay out the geometry of a part, and how a computer on the machine uses the design to guide the machine as it makes the part. But first we will give you a brief overview of numerical control (NC) in the field of machining. Figure 2-17.—Dot matrix printer. Figure 2-18.—Laser jet printer. NC   is   the   process   by   which   machines   are controlled by input media to produce machined parts. The most common input media used in the past were magnetic tape, punched cards, and punched tape. Today, most of the new machines, including all of those at Navy intermediate maintenance activities, are controlled by computers and known as computer numerical control (CNC) systems. Figure 2-19 shows a  CNC  programming  station  where  a  machinist programs a machine to do a given job. NC machines have many advantages. The greatest is the unerring and rapid positioning movements that are possible. An NC machine does not stop at the end of a cut to plan its next move. It does not get tired and it is capable of uninterrupted machining, error free, hour after hour. In the past, NC machines were used for  mass  production  because  small  orders  were  too costly.  But  CNC  allows  a  qualified  machinist  to program and produce a single part economically.