To place the coil in the E and W line, turn it until the pointers are at the 90° (90 degree) marks,--the 0° (zero degree) marks remaining, of course, as described above. =245. The Degree-Card, G D C= (Fig. 72) has a dot at its center, to show where to make a pin-hole for the pin that supports the compass-needle. With this you can tell how many degrees the needle is deflected when the current passes. This card, G D C, should be pressed down over the pin-point. The zero points of G D C should be N and S, also, when the coil is in that position; that is, they should be in the plane of the coil. The pointers on the needle (§ 246) will then be at O, when the needle is at rest, no current passing through the coils. (See Apparatus Book § 272 for Home-Made Degree-Card.) G D C may be held permanently in position after it is adjusted, by sticking a short pin through it into P P S. Do not let this pin interfere, however, with the swinging of the needle. [Illustration: Fig. 73.] =246. Pointers= (Fig. 73) should be fastened to the needle, in order to make the readings of degrees accurate. Fasten to the compass-needle a piece of No. 30 insulated copper wire, as shown. It may be cut to the proper length after it is wound around the needle. See that the wire does not touch the pin when needle is in place; balance needle by cutting a little from the heavier end of wire with shears; bend the ends of wire so that they are at opposite sides of the degree-card, both pointing at O, for example. The needle must swing freely, be nicely balanced, and the wire must not touch pin or degree-card. [Illustration: Fig. 74.] =247. Directions.= (A) Arrange as in Fig. 74, the coil being N and S (§ 244). Join the ends of the wires, 2 and 3, with the 5-turn coil of G V as shown. Wire, 2, is connected to L (Fig. 72). Press lever 2 of C R (Fig. 69) for an instant, watching the compass-needle and noting how many degrees it swings the first time. Get thoroughly in mind the direction in which the N pole of the needle is deflected when the current passes around G C in a "clockwise" direction. There must be no magnets, iron, or pieces of steel within 3 feet of A G. (B) Press lever, 3, for an instant, watching the needle. The current will now pass in an "anti-clockwise" direction. Is the needle deflected about the same number of degrees as in (A)? (C) Change the ends of the wires, 2 and 3, to the 10-turn coil (§ 242) and repeat (A) and (B). (D) Change 2 and 3 to L and R (Fig. 72), thus allowing the current to pass around 15 turns; then repeat (A) and (B).