Use a digital or physical engineering plan to learn engineering line standards. Scrutinize the plan and identify all of the "visible lines," which are the heavy, unbroken lines used to indicate the edge and shape of objects. Identify the "hidden lines" that are represented by medium lines with short, evenly spaced dashes used indicate the concealed edges of objects in the plan.
Locate the "center lines" that are comprised of long and short dashes alternately spaced and consistent in length and used to indicate symmetry about an axis and location of centers. Identify the "dimension lines" that are thin lines terminated with arrowheads at each end, used to indicate measured distance.
Locate the "extension lines" that appear as thin, unbroken lines used to indicate the extent of dimensions. Identify the "leaders" that are the lines that end with an arrowhead or a dot used to indicate a part, dimension or other reference. Locate "phantom" or "datum lines" that are a medium series of one long dash and two short dashes evenly spaced ending with a long dash.
Identify the "stitch lines" that are the medium lines of short dashes evenly spaced and labeled used to indicate stitching or sewing. Locate the "break" lines that are thin solid lines with freehand zig-zags used to convey a reduced size of the drawing required to represent the actual object and to reduce detail.