The changes that we have talked about created a wide variety of problems for amateur and professional genealogists alike. Because countries adopted these changes over several centuries, dates have been misinterpreted routinely. During your research you may find that many dates appear to have two years. This is not because the writer was unsure of the date but in fact, because both the Julian and Gregorian calendars were being used simultaneously. You may have noticed that a certain date in an English document was recorded as January 15, 1754/5. This is an example of the "double dating" technique, where the Julian calendar was 1754 and the Gregorian calendar was 1755. In Germany, this problem would have existed as early as 1544. Needless to say, this conversion from the "old style" to the "new style" and the double dating technique that resulted from it, must be carefully considered by the historian and recorded exactly as they are found to preserve the integrity of the record.

Another problem that we experience when recording dates is in the format that is used. In Europe, dates are typically recorded dd-mm-yyyy. You may also find that they are recorded as dd.mm.yy. In the United States, dates are recorded as mm-dd-yyyy or mm/dd/yyyy. I am confident that you have seen dates like 08/03/1995 where you are unsure if it refers to August 3 or March 8. Recently, the International Standards Organization introduced the ISO date standard of yyyy-mm-dd. Using this notation will ensure that everyone knows 1995/08/03 is August the third. There are a number all the advantages to using this notation. A few are as follows: