Date: 19 Elul 5581
From: Rabbi Moshe Sofer
To: Rabbi Meir Karnik
The responsum emphasizes the importance of accurate calendar calculations (molad and tekufah) for determining Jewish holidays and addresses the dangers of relying solely on printed calendars, citing past errors and the author's extensive work in this field.
Source: Shu"t Chasam Sofer Collected §35