A double date comes from the transition from the Julian calendar to the Gregorian calendar.
According to the Julian calendar, the first day of the year was March 25 and each year was 365 days and 6 hours long.
Not all areas accepted the change to the Gregorian calendar at the same time, however.
Because the Julian and Gregorian calendars were long used simultaneously, although in different places, calendar dates in the transition period were often ambiguous, unless it is specified which calendar was being used.
Images like these are so classic, they, for a number of people, are "as American as apple pie." They are produced and perpetuated by the media, through films like .
Because of these entertainment forums, these images will continue to be a pop cultural symbol of the 1950's.
Many Catholic countries switched over in 1582, but others waited much longer to switch over. Although this is related to the change from the Julian calendar to the Gregorian calendar the key issue that leads to the need for "double dates" is not that change, but rather the related change from starting the year on 25th March to starting it on 1st January.So a birth recorded in the period between 1st January and 25th March is shown as (e.g.) 3rd March 1733/4 to show that that the date intended was in March of the Civil Year 1733 and the Historical Year 1734, that is, the month before April 1734.There are other complications to do with calculation of leap years, and changeover from Julian to Gregorian calendars, but I believe I've covered the primary usage of 'double dates'.ORIGINS OF DATING Dating is definitely an "American phenomenon." Few other countries carry on this practice with as much fervor as Americans do.Then again, few other countries have the same social conditions as America.