Audio cables, man if there was only a standard! It used to be a breeze, XLR for professional balanced audio, 1/4" for mono audioand headphones, and RCA for line level unbalanced audio. Technology changes, and so did connector types! The days of standard zip cord for speakers is gone, 1/4" headphone jacks are rare, balanced audio has to plug into unbalanced audio and vice versa, and then of course there are DIN plugs, Speakon(TM) connectors, and various other connectors! It may never end, but this handy audio cable tester will make sure your connections are proper every time! Testing a cable is a breeze! Plug one end of it into the appropriate jack on the left side of the test box. Plug the other end of the cable into the other appropriate jack on the right side. Then select the rotary switch to "1" to test the connection of pin-1 of the cable. If a green LED lights there is a good connection of pin-1 with a yellow LED lighting above the connector used on the right side. No LEDs indicate an open or floating pin-1. Continue the same procedure by selecting "2" for pin-2, etc. until all contacts have been checked. If the Ground LED illuminates there is a connection from the selected pin to ground/shield/chassis. Two banana jacks are also provided to check test probes, AND to use the box as a continuity tester for other cables. Test probes are included! Runs on a standard9V battery. Measures 7.5" x 3.5" x 1.5" From Velleman