Each year, Nielsen processes approximately two million paper diaries from households across the country, for November, February, May, and July—also known as the "sweeps" rating periods. The term "sweeps" dates from 1954, when Nielsen collected diaries from households in the Eastern United States first; from there they would "sweep" west. Seven-day diaries (or eight-day diaries in homes with DVRs) are mailed to homes to keep a tally of what is watched on each television set and by whom. Over the course of a sweeps period, diaries are mailed to a new panel of homes each week. At the end of the month, all of the viewing data from the individual weeks is aggregated. One exception to the normal sweeps periods occurred in 2008–09 when the February sweeps period was moved to March to accommodate the digital television transition, which was scheduled to take place on February 17, 2009. The transition date was moved to June 12, but Nielsen stayed with the March sweeps period.