The standard differentiates among telephone worker (WG-9), telephone mechanic (WG-10), and telephone mechanic (WG-11) in terms of duties, skill and knowledge, responsibility, physical effort, and working conditions. All are involved in installing, modifying, repairing, and maintaining telephone systems. The work requires knowledge and telephone equipment and installation procedures; knowledge of basic electrical principles as they pertain to the telephone system; the ability to understand and follow such technical guidance as circuit descriptions schematics and layout sheets; and the ability to locate and repair trouble within the telephone system. (AG)