The ghosts could then be traced and the tracings were used to produce very accurate reproductions of the missing Madison-era locks.  Close, and even exact, reproductions could be created from these tracings because in the late 18th and early 19th centuries almost all door locks, handles, and other door hardware were standardized and mass produced in small factories.  Much of the hardware was also being produced in England and then imported into the United States.  Because England was supplying much of the young United States with hardware during this period, very little variation in door locks is seen from region to region during the late 18th and early 19th centuries.