7]
With a fifteen-tooth escape wheel each tooth occupies twenty-four
degrees, and from the point _f_ to _e_ would be two and one-half
tooth-spaces. We show the dotted points of four teeth at _D D' D''D'''_.
To establish the center of the pallet staff we draw a line at
right angles to the line _p e'_ from the point _e_ so it intersects the
line _f h_ at _k_. For drawing a line at right angles to another line,
as we have just done, a hard-rubber triangle, shaped as shown at _C_,
Fig. 7, can be employed. To use such a triangle, we place it so the
right, or ninety-degrees angle, rests at _e_, as shown at the dotted
triangle _C_, Fig. 6, and the long side coincides with the radial line
_p e'_. If the short side of the hard-rubber triangle is too short, as
indicated, we place a short ruler so it rests against the edge, as shown
at the dotted line _g e_, Fig. 7, and while holding it securely down on
the drawing we remove the triangle, and with a fine-pointed pencil draw
the line _e g_, Fig.
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