XProfan

Windowtitle "Einfache Näherungsformeln for Islamisches and Jüdisches Kalenderjahr"
' Q: https://de.wikipedia.org/wiki/Islamische_Zeitrechnung#Umrechnung
' Q: https://de.wikipedia.org/wiki/J%C3%BCdischer_Kalender
' OHNE JEDWEDE GEWÄHR!
Window Style 24:cls:font 2:declare j&
repeat :Print "\n   Jahreszahl to Gregorianischem Calendar:  ";:input j&
print "\n year to Islamischer Zeitrechnung vaguely:  ";int(0.5+32/33*(j&-622));
print "\n year to Modern-Jüdischer Zeitrechnung ca:  ";int(365.2468/365.2425*(j&+3760+(j&<=0))+.5);"\n"

until %key=27

End

Schaltjahrsregeln not very enough?
==========================
The Gregorianische Calendar sorgte known for, that the Julianische date 4. Okt. 1582 the gregorianische date 15. Okt. 1582 followed. target was thereby, whom 21. March each year (Frühlingsbeginn) again on the astronommisch-natural Frühlingspunkt (sunrise very in the east) To schieben, How the The high katholischen dignitaries on the Konzil of Niccäa einst set had. The good solid was from the helms run, because the Sonnenjahr (Frühlingspunkt-Durchlauf To Frühlingspunkt-Durchlauf) even still not 365,25 days lasts, separate only 365,2425 plus a couple zerquetschte Nachkommastellen. The new rule of pope Gregor, that any 400 years DOCH one leap-year his ought to, behob the disaster einstweilen.

unfortunately summiert itself the remainder but in the running of 3300 years still on a whole day. Vorausschauende Astronomen hit[ed] therefore to, The thing with the stupid Schaltsekunden (up to 2 per year, sh.  [...]  still finally his To let and for The years 4800, 8000 and 11200 still no leap-year his To let. Well, there does us nothing More painful ...

P.s.: The gregorianische Calendar watts not all Ländern at the same time introduced, separate this process pulled itself over several centenaries, see  [...]