e one with the
other by measuring each step, because one step would require to be
pencilled in before the next could be marked. To avoid this the centre
line 1, Figure 134, is first marked, and the arcs for the steps are then
marked as shown. Centre lines are also necessary to show the alignment
of one part to another; thus in Figure 135 is a cube with a hole passing
through it. The dotted lines in the side view show that the hole passes
clear through the piece and is a parallel one, while the centre line,
being central to the outline throughout the piece, shows that the hole
is equidistant, all through, from the walls of the piece.

[Illustration: Fig. 134.]

[Illustration: Fig. 135.]

The pencil lines for this piece would be marked as in Figure 136, line 1
representing the centre line from which all the arcs are marked. It will
be noted that the length of the piece is marked by arcs which occur,
because being a cube the set of the compasses for arcs 2, 3, 4 and 5
will answer without altering to mark arcs 6 and 7.

[Illustration: Fig. 136.]

If the hole in the piece were a taper or conical one, it would be
denoted by the dotted lines, as in Figure 137, and that the taper is
central to the body is shown by these dotted lines being equidistant
from the centre line.

[Illustration: Fig. 137.]

Suppose one of the sides to be tapered, as is the side A, in Figure 138,
and that the hole is not central, and both facts will be shown by the
centre lines 1 and 2 in the figure. The measurement of face A would be
marked from A to line B at each end, but the distance the hole was out
of the centre would be marked by the distance between the centre line 2
and the edge C of the piece.

[Illustration: Fig. 138.]

If the hole did not pass entirely through the piece, the dotted lines
would show it, as in Figure 139.

[Illustration: Fig. 139.]

[Illustration: Fig. 140.]

The designations of the views of a piece of work depend upon the
position in which the piece stands, when in place upon the machine of
which it forms a part. Thus in Figure 140 is a lever, and if its shaft
stood horizontal when the piece is in place in the machine, the view
given is an end one, but suppose that the shaft stood vertical, and the
same view becomes a plan or top view.

[Illustration: Fig. 141.]

[Illustration: Fig. 142.]

In Figure 142 is a view of a lever which is a side view if the lever
stands horizontal, and lever B hangs down, or a