How I am calculating the Hijri Calendar
Right now I am following the procedure bellow.
For hijri year 1370 and after wards. Moon age should be 9 hours at sun set in Mecca.
And for years before 1370 I am following Yollop's crescent visibility formula. This extends upto Hijri 1st.
This one is looking very promising as it more closely matches to what Saudi Government declares each year.