<P> Until the latter part of the 20th century, all architectural drawings were manually produced, if not by the architects, then by trained (but less skilled) draughtsmen (or drafters), who did not generate the design, but did make many of the less important decisions . This system has continued with CAD draughting: many design architects have little or no knowledge of CAD software programmes, relying upon others to take their designs beyond the sketch stage . Draughtsmen often specialize in a type of structure, such as residential or commercial, or in a type of construction: timber frame, reinforced concrete, prefabrication, etc . </P> <P> The traditional tools of the architect were the drawing board or draughting table, T - square and set squares, protractor, compasses, pencil, and drawing pens of different types . Drawings were made on vellum, coated linen, and tracing paper . Lettering would either be done by hand, mechanically using a stencil, or a combination of the two . Ink lines were drawn with a ruling pen, a relatively sophisticated device similar to a dip - in pen, but with adjustable line width, capable of producing a very fine controlled line width . Ink pens had to be dipped into ink frequently . Draughtsmen worked standing up, keeping the ink on a separate table to avoid spilling ink on the drawing . </P> <P> Developments in the 20th century included the parallel motion drawing board, as well as more complex improvements on the basic T - square . The development of reliable technical drawing pens allowed for faster draughting and stencilled lettering . Letraset dry transfer lettering and half - tone sheets were popular from the 1970s until computers made those processes obsolete . </P> <P> Computer - aided design is the use of computer software to create drawings . Today the vast majority of technical drawings of all kinds are made using CAD . Instead of drawing lines on paper, the computer records equivalent information electronically . There are many advantages to this system: repetition is reduced because complex elements can be copied, duplicated and stored for re-use . Errors can be deleted, and the speed of draughting allows many permutations to be tried before the design is finalised . On the other hand, CAD drawing encourages a proliferation of detail and increased expectations of accuracy, aspects which reduce the efficiency originally expected from the move to computerisation . </P>

Any kind of line drawing that shows the most important properties of an object is called a