The tester is a 3-pin standard xlr and has three l.e.d.s displaying the varied faults. Basically all 3 led's on and/or flashing is good. The red and green led's show the positive and negative poles of the data stream, the yellow led shows the earth insulation and the refresh rate of the data stream. This is the tester that the professionals use to determine faults with dmx circuits. Works with any desk, dimmer or light that uses dmx including Avolites, high-end, martin, clay paky, coemar, vari*lite, pulsar to name but a few. The picture shows the 5-pin version, the 3-pin uses a different make of xlr shell. Now comes with a lanyard to hang it round your neck or off a tool belt...