Early German dates

I am researching in the Maxsain,Rheinland-Pfalz area and have run into
a problem with the dates in the records. As an example, they are
written in the following format: Jacob Leonhardi died Sunday 21/15
March 1685, buried Monday AB/AB. Can anyone help me in finding what
this translates to or where I can find information on this type of
date entry? Thanks.....sherman...........

Bernd Mayer...

Because of the fact that the durance of a year doesn't exactly match the
counting of the Calendar the Catholic Church decided to reform the old
julian calendar. To the new date there had to be added 10 days and for
the reason the calendar not running out of the rhythm of the year again
they also decided to leave out a few leap days. So far the problem.

Between 1582 where the gregorian Calendar (the reformed julian Calendar)
was first introduced and 1700 in germany both calendars were in use.
One way to express which date wa meant was to write the new style in the
numerator, the old style into the denominator of a fraction. But it
could also exist the other way round.

What does not corrspond with my assertion is the combination 21/15. For
the year 1685 the difference between julian and gregorian date should be
10 days. But I nevertheless believe that it must have to do with the
gregorian Calendarreform. The reform causes effects like this and I
don't know an other event in that time that could have made such an
effect. Perhaps it is only a mistake in reading of the script or in
writing of the writer.

so far
greetings

Bernd Mayer

references:
Grotefend, Hermann: Taschenbuch der Zeitrechnung; 13.Auflage 1991;
Hannsche Buchhandlung; Hannover.