GVS139B can accurately and quickly determine the positive and negative polarities of the speaker unit, each speaker in the loudspeaker, the earphone, and the receiver in a noisy environment. The positive and negative polarities are displayed with the aid of sound and lighting. Its operation is simple and no misjudgment is possible.

There are three sets of external input terminals and touch switch selectors to cooperate with other instruments to test the characteristics of speakers, which can greatly improve the productivity.

It can also accurately determine the polarity when used in a noisy environment (e.g. production line).