Definition of Saeculum
The web page does not have an explicit definition of Saeculum. It appears to be two nine-year periods each with the 3 extra months. I reckoned the number of days in each such period to 9*73*30+31+27+31 = 19809 days, which lasts around 54 years. so seems to form half a Saeculum, which is stated as 108 years. I also calculated 3 Saros periods to last about 19756 days.
Karl Palmen (talk) 15:17, November 8, 2019 (UTC)
I did further calculations and now I think the 3 extra months are added once every 18 years to form one saeculum and also they normally have 31, 30, 31 days (not 31, 27, 31). This gives 18*73*30+31+30+31 = 39512 days, which is the correct number of days in 6 Saros cycles (223*29.5306 = 39511.9428).
Karl Palmen (talk) 16:19, November 8, 2019 (UTC)