A tool is an implement or device used directly upon a piece of material to shape it into a desired form. Hand tool,s any of the implements used by craftspersons in manual operations, such as chopping, chiseling, sawing, filing, or forging. Complementary tools, often needed as auxiliaries to shaping tools, include such implements as the hammer for nailing and the vise for holding. A craftsperson may also use instruments that facilitate accurate measurements: the rule, divider, square, and others. Power tools—usually handheld motor-powered implements such as an electric drill or electric saw—perform many of the old manual operations and as such may be considered hand tools.