Drawing-office work is divisible into four principal groups. First, there is the actual designing, by far the most difficult work, which is confined to relatively few well-paid men. The qualifications necessary for it are a good scientific, mathematical and engineering training, and a specialized experience gathered in the particular class of mechanism to which the designing relates. Second, there is the work of the rank and file who take instructions from the chiefs, and elaborate the smaller details and complete the drawings. Third, there are the tracers, either youths or girls, who copy drawings on tracing paper without necessarily understanding them. Fourth, there is a printing department in which phototypes are produced on sensitized paper from tracings. The character of the drawings used includes the general drawings, or those which show a mechanism complete; and the detailed drawings, which illustrate portions isolated from their connexions and relationships. The first are retained in the office for reference, and copies are only sent out to the men who have to assemble or erect and complete mechanisms. The second are distributed to the several shops and departments where sectional portions are being prepared, as pattern shop, smithy, turnery, machine shop, &c. General drawings are, as a rule, drawn to a small scale, ranging say from 1/8 in. to 1 in. to the foot; but details are either to actual size, or to a large scale, as from 1½ in. to the foot or 3 in. or 6 in. to the foot. A large number of minutiae are omitted from general drawings, but in the detailed ones that are sent into the shops nothing is apparently too trivial for insertion. In this respect, however, there is much difference observable in the practice of different firms, and in the best practice of the present compared with that of former years. In the detailed drawings issued by many firms now, every tiny element and section is not only drawn to actual size, but also fully dimensioned, and the material to be used is specified in every case. This practice largely adds to the work of the drawing-office staff, but it pays.