This section is from the book "Spons' Mechanics' Own Book: A Manual For Handicraftsmen And Amateurs", by Edward Spon. Also available from Amazon: Spons' Mechanics' Own Book.
The chalk line is used as shown in Fig. 242 for the purpose of marking where cuts have to be made in wood. It consists of several yards of cord wound on a wooden reel, and well rubbed with a piece of chalk (or charcoal when a white line would be invisible) just before use. In applying it, first mark with the carpenter's pencil the exact spots between which the line is to run, then pass a bradawl through a loop near the end of the cord and fix it firmly in the wood at the first point marked, next apply the chalk or charcoal to the cord, or as much of it as will suffice for the length of line to be marked, this done, stretch the cord tightly to the second point marked, and either fasten it by looping it round a second bradawl, or hold it very tightly in the finger and thumb of one hand, whilst with the finger and thumb of the other hand you raise, it in the middle as much as it will stretch; on suddenly releasing it, it springs back smartly and leaves a well-defined line between the two points.
The novice may find it helpful to mark both sides of his work, which is best done by removing the cord without disturbing the bradawls.