it is
so essential to secure the most minute economies in manufacture that the
first articles made are of a more or less experimental character. Only
after no further improvement seems for the time being possible are the
drawings made or completed for standard use and reference. In some
modern shops even standardized drawings are scarcely used, but their
place is taken by the templets, jigs and fixtures which are employed by
the workmen as their sole guides in machining and assembling parts. By
the employment of these aids locations and dimensions are embodied and
fixed absolutely for any number of similar parts; reference to drawings
thus becomes unnecessary, and they therefore fall into disuse.

The mechanical work of the drawing office is confined strictly to
orthographic projections and sections of objects. Perspective views are
of no value, though occasionally an object is sketched roughly in
perspective as an aid to the rapid grasp of an idea. Drawings involve
plans, elevations, and sectional views, in vertical and angular
relations.

There are a good many conventionalities adopted which have no
correspondences in fact, with the object of saving the draughtsman's
time; or else, as in the case of superposition of plans and sections, to
show in one view what would otherwise require two drawings. Among the
convenient conventionalities are the indications of toothed wheels by
their pitch lines only, of screws by parallel lines and by diagonal
shade lines; and of rivets, bolts and studs by their centres only. The
adoption of this practice never leads to error.

In the preliminary preparation of drawings in pencil no distinction is
made between full or unbroken lines, and dotted or centre lines, and the
actual outlines of the objects. These differences are made when the
inking-in is being done. Indian or Chinese ink is used, because it does
not run when colours are applied. There are conventional colours used to
indicate different materials. But colouring is not adopted so much as
formerly, because of the practice of making sun prints instead of the
more expensive tracings for the multiplication of drawings. When
tracings are coloured the colour is applied on the back instead of on
the side where the ink lines are drawn.

The economical importance of the printing department of the drawing
office cannot be overestimated. Before its introduction drawings could
only be reproduced by laborious tracing on paper or cloth,