In the production of varistors, diode chips are cut from a p-n sheet-diffused semiconductor wafer. Instead of having conventional rectangular shapes, the chips have a rhomboidal shape. This makes the shape of the chips asymmetric in that one surface of each chip becomes a distinguishable mirror image...http://www.google.com.au/patents/US4253280?utm_source=gb-gplus-sharePatent US4253280 - Method of labelling directional characteristics of an article having two opposite major surfaces
