With a short piece of wire connect the hinge post of the testing key marked “cable” to either “earth” post of the key, the leads to the cable tank being disconnected at E, B, and P. Turn the shunt to 0. Examine the ⅒ megohm box and see that all the resistance coils are in the circuit. Close the battery switch and the testing key. Turn the shunt to the ¹/₁₀₀₀ post. Watch the swing of the galvanometer and when it has come to rest, read and record. Turn the shunt to 0. The galvanometer should return exactly to 0. If it does not, readjust and repeat until it does. The galvanometer constant is numerically equal to the total throw in _smallest_ divisions of the scale multiplied by 100. Remove the connecting wire and replace the leads to the tank. If at any subsequent time during the test the galvanometer adjustment is disturbed—that is, if it does not return accurately to zero when the shunt is at 0—the constant should be redetermined. =Testing the cable.=—1. See that the testing key is open and the shunt at 0. Connect the earth lead to ground on the cable armor. Remove the earth connection from No. 1 conductor and connect the cable lead to this conductor; in wet weather the connector joint should be dipped in melted paraffin. (In using paraffin to insulate joints or ends bring it just above 212° F. to evaporate any moisture present. It should not be boiling. The paraffin coating should be at least as thick as the rubber insulation and extend back over the rubber for an inch or more.) 2. Close the testing key to the left (+ to earth), stopping at the discharge position, and turn the shunt to the unity post. There should be no deflection. If there is, it is due either to a charge on the cable, which will disappear after a moment, or to earth currents. (It is assumed that the testing apparatus has been thoroughly tested for insulation.) If due to earth currents, the conductor is probably a poor one. Earth currents are readily recognizable by their fluctuating character. Before assuming that the trouble can not be removed, the joint between the lead and the conductor should be examined again. Moisture on the cable end will give a path for earth currents. Note the value and direction of the throw of the galvanometer and record it. 3. Turn the shunt to 0, close the testing key all the way down (+ to earth), noting the time to the second, or starting the stop watch at the same time, if one is available. The time must be accurately noted. The insulation resistance at the end of one minute’s electrification is the resistance to be reported.