A datum line is a line used to indicate a line or plane of reference, such as the plane from

Figure 3-39.-Use of an offset section.

which an elevation is measured. Datum lines consist of one long dash and two short dashes (medium thickness), equally spaced. Datum lines differ from phantom lines only in the way they are used.

Stitch lines are used to indicate the stitching or sewing lines on an article. They consist of a series of very short dashes (medium thickness), approximately half the length of the dash of hidden lines, evenly spaced. Long lines of stitching may be indicated by a series of stitch lines connected by phantom lines.

Match lines are used when an object is too large to fit on a single drawing sheet and must be continued on another sheet. The points where the object stops on one sheet and continues on the next sheet must be identified with corresponding match lines. They are medium weight lines indicated with the words construction drawings that may require match lines are maps and road plans where the length is much greater than the width and it is impractical to reduce the size of the drawing to fit a single sheet.