A gloved hand holding a processed silicon wafer. The wafer contains over 200 complete electronic 'chips'. The three black rectangles on the wafer contain test circuits and components, such as resistors and capacitors. As the wafer passes through its production stages, these circuits are checked to ensure correct and consistent deposition or etching of the various layers. In the early stages of manufacture, errors in etching may be corrected to some extent, but more often the wafer is rejected.