A wiggler, wobbler or edge-finder is a tool used in a milling machine or machining centre. The device is used to accurately determine edges or markings and therefore the centre of a work piece or a previously machined feature during the set-up phase of a machining operation. Electronic edge finders can locate edges of work pieces and also height offsets. It works in a non-rotating spindle, which is a great advantage over its mechanical counterparts. It is battery operated and works by lighting up its internal LED (usually red) when the electrical circuit formed by the instrument, the work piece and the machine is closed. The light is illuminated when the edge finder is touching the work piece and is visible through openings in the case.