A bi-directional electrostatic discharge diode structure consumes substantially less silicon real estate and provides ultra-low capacitance by utilizing a p\u2212 epitaxial layer that touches and lies between an n+ lower epitaxial layer and an n+ upper epitaxial layer. The shaped superior and inferior light stimuli stimulate pupillary responses whose amplitudes are measured. The light source emits a combined light beam that is emitted by a first laser and a second laser. Such a method bypasses the basic materialization of the distance between objects. A one-piece ring gear having a diameter less than or equal to the diameter of the grinding tube is attached to the small diameter end of a discharge cone of the grinding tube.