AAll DCA-20PC dc ammeters are designed to measure the current flowing through an external ‘load’. This load could be something as simple as a dc motor, a light bulb, a heater, or it could be a complex piece of test equipment. The current drawn by the external load (i.e., the current the ammeter will measure and display) enters TB1-1, develops a small millivolt signal across an internal shunt, and then flows out of TB1-2 to the load.