An ammeter (Fig. 80) is simply a commercial form of galvanometer. It is constructed in the same way, but only a small fraction of the current to be measured passes through the coil. The greater portion passes through the shunt, which is located in one of the leads coming from the machine. The terminals on the shunt are connected to the terminals on the ammeter by a pair of flexible leads about 10 ft. long. After the ammeter is made, it is tested by operating one machine on a certain number of lamps at exactly 110 volts and then throwing off that machine and operating the same number of lamps with another machine. If readings on the ammeter are the same, it is correct.