Spathaky,
Mike Old Style New Style dates and the change to the Gregorian calendarArhivirano 2008-11-21 na Wayback Machine-u. "An oblique stroke is by far the
most usual indicator, but sometimes the alternative final figures of
the year are written above and below a horizontal line, as in a
fraction (a form which cannot easily be reproduced here in ASCII text).
Very occasionally a hyphen is used, as 1733-34."
Roscoe Lamont,
"The Roman calendar and its reformation by Julius Caesar", Popular Astronomy27
(1919) 583–595. The reference is the second article in the hyperlink;
its last page is here. Sacrobosco's theory is discussed on pages 585–587.
Spathaky,
Mike Old Style New Style dates and the change to the Gregorian calendarArhivirano 2008-11-21 na Wayback Machine-u. "An oblique stroke is by far the
most usual indicator, but sometimes the alternative final figures of
the year are written above and below a horizontal line, as in a
fraction (a form which cannot easily be reproduced here in ASCII text).
Very occasionally a hyphen is used, as 1733-34."
