I recently repaired a Schatz 1000 day clock made in 1960. As I removed the mainspring from the barrel, I realized how excellent this mainspring is. It opens very far, showing no sign of fatigue. In fact, nearly every 1000 day clock I’ve repaired has a similar spring. A mainspring like this will last for many more years, and should be retained in the clock (not replaced).
The left photo below shows the mainspring and the brass barrel that contains it. This mainspring is original to the clock. This mainspring can run the clock for nearly 3 years on one winding.
Job 6178. Polished 7 pivots and replace the suspension spring. The movement has the date 3 60 (March 1960) on the back. Horolovar back plate no. 1010A. 0.0024 inch thick suspension spring.