Description: The Romans designed the censuses as a way of keeping track of their subjects, and this 'snapshot' approach has been continued, very inefficiently, to the present day. Primary care commissioners in Newham despair their data is already five years old, while DVLA driver data might almost be up-to-the-minute. The decennial census made it easy for people to disappear, and the family historian someday needs to win the battle of the crack. My emigrant cousins have children: Barnaby Hooper, Sophia Thynne, Mary Perry who leave England as youngsters before the census nets them. Mary's mother was a childless widow returned from Australia in 1851, and by 1861 was back out there with Mary and her new family. See what a difference a decade makes.