The spread of clocks and watches linked people by getting their schedules into phase; thus timekeepers served as agents of social organization, enabling groups to live and work with the reliability of automata. Manufacture in bulk-by teams, as opposed to lone craftsmen-depended on regularity and repetition in process and supplies. Coordination spread by factory bell and whistle, then by company clock, then by individual watches. Karl Marx wrote Frederick Engels in 1863, "The clock is the first automatic machine applied to practical purposes; the whole theory of production of regular motion was developed through it." No wonder some historians describe the spread of timekeeping in terms of dehumanization and enslavement. "In the mechanized factory men are synchronized to machines, which in general have more regular habits than men," writes Sebastian de Grazia. "Materials too have to flow to feed the machines, and thus a synchronization of men, machines, and materials develops, more impersonal and complex than anything before. Most men today may not be aware that they are geared to machines-even while they are being awakened by the ringing of a bell and gulping down their coffee in a race with the clock."