3. It should be explained, the part cut from the sheet brass is shown
below the dotted line _k_, the portion above (_C_) being a round handle
turned from hard wood or ivory. The slot _l_ is sawn in, and two holes
drilled in the end to insert the needle points _i i_. In making the slot
_l_ we arrange to have the needle points come a little too close
together to agree with the degree spaces on the arcs _a a_ and _b b_. We
then put the small screw _j_ through one of the legs _D''_, and by
turning _j_, set the needle points _i i_ to exactly agree with the
degree spaces. As soon as the points _i i_ are set correctly, _j_ should
be soft soldered fast.
The degree spaces on _A_ are set off with these dividers and the spaces
on _A_ very carefully marked. The upper and outer arc _a a_ should have
the spaces cut with a graver line, while the lower one, _b b_ is best
permanently marked with a carefully-made prick punch. After the arc _a a_
is divided, the brass plate _A_ is cut back to this arc so the
divisions we have just made are on the edge.
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