The mechanical engineering industry is at once one of the most important of modern industries, and one of the most difficult to define. The first British Census of Production, taken in 1907, classified the output of the engineering industry (including electrical engineering) under forty separate headings; even these headings are often merely broad descriptions – for example ‘agricultural machinery’, ‘textile machinery’, ‘railway and tramway equipment and parts’ – which conceal the operations of hundreds of firms producing thousands of separately named pieces of equipment (P.P. 1912–13b). Perhaps the most important single unifying factor, linking these thousands of disparate products, however, is that the mechanical engineering industry is concerned with the processing of metals, and in particular with the transformation of metals into machinery, for further use in the operations of a myriad other industries. This transformation of raw or semi-finished metals into machinery is carried out by machine tools, defined ‘as briefly as possible’ by one writer as

The machine tool industry thus occupies a central place within the mechanical engineering industry.