Before 1752, the English government observed the Julian calender and March 25 as the first day of the new year. On March 25, 1752 the English government and the American colonies switched to the Gregorian calendar. On Sept. 14 1752 the following day was Sept. 2, 1752. You lived 13 days over again. This adjustment was necessary to sync the calendar with the religious holidays which were getting out of wack due to the errors in the Julian time keeping system. There are many expert explanations of both the calendar systems on the internet. Just type Julian calendar or Gregorian calendar into Google or any internet search engine. Or look in the help files of most genealogy software. To the question: So if the Julian date is 29 7 mon 1683. The Gregorian date is 29 Oct 1683 by my calculation. I just add 3, this may not be exactly the right to do it.