A double date appears on some documents as a result of two changes introduced by the adoption of the Gregorian calendar, introduced by Pope Gregory XIII in 1582 to resolve the error caused by the Julian calendar in use up to that time. Scientists resolved that a year was slightly longer than the 365 ¼ specified by the Julian calendar, which resulted in the loss of 10 days. The new calendar also changed the first day of the year from March 25th on the Julian calendar to January 1st. Different countries adopted the new calendar at different times and the practise of providing a double date was common. The British Commonwealth and the United States adopted the new calendar in 1752. By this time, the calendar was behind by 11 days. So, the day following September 2, 1752 was decreed to be September 14, 1752. .