2008TCVN 8-21-2005 Technical drawings.General principles of presentation.Part 21:Preparation of lines by CAD systems.
2002TCVN 8-20-2002 Technical drawings.General principles of presentation.Part 20:Basic conventions for lines
TCVN 8-20-2002 Technical drawings.General principles of presentation.Part 20:Basic conventions for lines was changed to TCVN 8-21-2005 Technical drawings.General principles of presentation.Part 21:Preparation of lines by CAD systems..