Mechanical engineers design, develop and make tools, machines and other mechanical devices. They are involved in this process from the initial design right through to the manufacture and installation of the final product. Mechanical engineers can work on a variety of projects, from designing mechanical hearts used in the medical industry, to car engines, through to designing and improving the production processes at mine sites. When designing machines they must take into account the cost to build and run a finished design, availability of materials and strength and maintenance requirements. To ensure the necessary standards are met they must regularly test designs, which can involve building a working prototype, and making necessary adjustments based on its performance.