@misc{Ideler_Ludwig_Lehrbuch_1831,
 author={Ideler, Ludwig},
 address={Berlin},
 howpublished={online},
 year={1831},
 publisher={August Rücker},
 language={ger},
 title={Lehrbuch der Chronologie},
 keywords={chronology textbook, the synodic month, Julian calendar, Gregorian calendar},
}