1. Primitive Time-Reckoning;Nilsson,1920
2. Chronology of Ancient Nations;Al-Biruni,1879
3. On the earliest visibility of the lunar crescent in the evening sky;Schmidt;Astr. Nachr.,1968
4. Chronologie;Mommsen,1883
5. On the smallest visible phase of the moon;Fotheringham;Mon. Not. R. astr. Soc.,1910