


If the original is one that is to be preserved, and might be marred by the guide lines, one of these methods should be used:
(i) Tack a piece of very transparent tracing paper (the vegetable tracing paper is preferable for this purpose) over the- original and place the guide lines on the tracing paper.
(2) Use tracing gelatine instead of paper and a steel point instead of a pencil, and with the latter scratch the guide lines on the gelatine. A coarse needle fastened into a cork as a handle makes a good tracing point.
(3) If the copy is very large pins may be placed at the points where the usual vertical, horizontal and oblique lines intersect the outer lines and thread carried from one point to the other instead of marked lines.