Disputes over whether the Scientific Revolution contributed to the Industrial Revolution begin with the common assumption that natural philosophers and artisans formed radically distinct groups. In reality, these groups merged together through a diverse group of applied mathematics teachers, textbook writers and instrument makers catering to a market of navigators, gunners and surveyors. From these "mathematical practitioners" emerged specialized instrument makers whose capabilities facilitated industrialization in two important ways. First, a large supply of instrument and watch makers provided Britain with a pool of versatile, mechanically skilled labour to build the increasingly complicated machinery of the late eighteenth century. Second, the less well known but equally revolutionary innovations in machine tools-which, contrary to the Habbakuk thesis, occurred largely in Britain during the 1820s and 1830s to mass produce interchangeable parts for iron textile machinery-drew on a technology of exact measurement developed for navigational and astronomical instruments.