On Wed, 15 Feb 2017, Ignacio Diaz-Emparanza wrote:
Oh! I have it. Gretl is considering 1700 as a leap year, when it is
not so.
The exact centuries are only leap years when they are a multiple of 400.
Gretl follows the unix "cal" program on this. In lib/src/calendar.c:
/* leap year -- account for gregorian reformation in 1752 */
#define leap_year(yr) \
((yr) <= 1752 ? !((yr) % 4) : \
(!((yr) % 4) && ((yr) % 100)) || !((yr) % 400))
See also
https://www.timeanddate.com/calendar/index.html?year=1700
Allin