sentences:  By sweeping the voltage through the configured range of main terminal voltages, for each voltage step of the control signal, a group of V-I curves is generated automatically.This group of curves makes it very easy to determine the gain of a transistor, or the trigger voltage of a thyristor or TRIAC.Curve tracers usually contain convenient connection arrangements for two- or three-terminal devices, often in the form of sockets arranged to allow the plugging-in of the various common packages used for transistors and diodes.