Making things requires a great variety of tools. The growth of technology in general has been greatly helped by improvement in the fineness and sharpness of cutting tools, the force that can be applied, the temperature at which heat can be concentrated, the swiftness with which operations can occur, and the consistency with which operations can be repeated. Such tools are an essential factor in modern manufacturing, which is based largely on the need to produce great numbers of products of uniform quality (such as automobiles and wristwatches) and much smaller numbers of products of extremely high quality (such as space vehicles and atomic clocks). Modern manufacturing processes usually involve three major steps: (1) obtaining and preparing raw materials; (2) mechanical processing such as shaping, joining, and assembling; and (3) coating, testing, inspecting, and packaging. In all of these steps, there are choices for how to sequence tasks and how to perform them, so the organization of tasks to optimize productivity is another major component of manufacturing. Modern factories tend to specialize in making specific products. When a large number of nearly identical things are made on a continuous basis at the same place, it is possible to make them much more cheaply than if they were made separately. Such cost-effectiveness is achieved by bringing workers together with machines, energy sources, and raw materials or component parts. The maintenance and repair of products are also likely to be easier when production is centralized because parts can be made that are interchangeable between units and even between different models.