Material: Plastic Color: Black Size: 10.5cm x 7cm x 2.5cm/ 4.1" x 2.8" x 1.0"(L*W*H) Applicable: the speaker phase and the amplifier output phase testing. Set-up for car audio system of speakers and amplifiers. Method of Application: This CD include 4 section test music: section 1: left channel noise signal section 2: right channel noise signal section 3 and section 4: phase test signal Put it in car CD player, and play section 1 or 2, can check the left/right channel connection is right or not. Play the section 3 or 4, the sound speaker will produce a fixed frequency signal. then press the test button on the phasemeter, 3 green light flash and 1 red light indicates that the speaker output is in positive phase (correct connection) ; 3 red light flash and 1 green light indicates that the speaker output is in negative phase (reversed connection).