1.
A wooden box, D, is then made and provided with a glass front. A
piece of paper is pasted on a piece of wood, which is then
fastened in the box in such a position that the hand or pointer
will lie close to the paper scale. The box is 5-1/2 in. high, 4
in. wide and 1-3/4 in. deep, inside measurements. After everything
is assembled put a drop of solder on the loop at D, Fig. 5, to
prevent it turning on the axle.
To calibrate the instrument connect as shown in Fig. 7, where A is
the homemade ammeter; B, a standard ammeter; C, a variable
resistance, and D, a battery, consisting of three or more cells
connected in multiple. Throw in enough resistance to make the
standard instrument read 1 ohm [sic: ampere] and then put a mark
on the paper scale of the instrument to be calibrated. Continue in
this way with 2 amperes, 3 amperes, 4 amperes, etc., until the
scale is full. To make a voltmeter out of this instrument, wind
with plenty of No. 36 magnet wire instead of No. 14, or if it is
desired to make an instrument for measuring both volts and
amperes, use both windings and connect to two pairs of binding
posts.
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