A Talk By Peter Edwards: We delve into the historical misalignment caused by theJulian Calendar, which, over the centuries, accumulated a discrepancy of 10 days. This anomaly was finally corrected in 1582 with the adoption of the Gregorian Calendar. The talk  examines how these lost ten days were addressed, the key individuals whose work enables this significant calendar reform, and the equipment and methods employed in aligning timekeeping with astronomical observation.