<P> Traditional and typical styli used for technical drawing are pencils and technical pens . </P> <P> Pencils in use are usually mechanical pencils with a standard lead thickness . The usual line widths are 0.18 mm, 0.25 mm, 0.5 mm and 0.7 mm . Hardness varies usually from HB to 2H . Softer lead gives a better contrast, but harder lead gives a more accurate line . Bad contrast of the lead line in general is problematic when photocopying, but new scanning copy techniques have improved the final result . Paper or plastic surfaces require their own lead types . </P> <Table> <Tr> <Th> "Drawing pens" </Th> </Tr> <Tr> <Td> <Table> <Tr> <Td> </Td> </Tr> <Tr> <Td> A traditional ruling pen, already in use in the 1600s . </Td> </Tr> </Table> <Table> <Tr> <Td> </Td> </Tr> <Tr> <Td> Grafos stylus . </Td> </Tr> </Table> <Table> <Tr> <Td> </Td> </Tr> <Tr> <Td> A disassembled Grafos and nibs of different widths . </Td> </Tr> </Table> <Table> <Tr> <Td> </Td> </Tr> <Tr> <Td> Rapidograph styli of different widths: 0.35, 0.5 and 0.7 mm . </Td> </Tr> </Table> <Table> <Tr> <Td> </Td> </Tr> <Tr> <Td> Rapidograph stylus parts . The head can be further disassembled . </Td> </Tr> </Table> </Td> </Tr> </Table> <Tr> <Th> "Drawing pens" </Th> </Tr>

What is the primary difference between the pen tool and the pencil tool