When I saw the two frequency actuator I assumed the 12:00 sub-dial was the PR indicator, but I always roughly thought the beat frequency was directly proportional to the the power reserve; meaning if the watch beats 4X faster, the power reserve would appr...
At 5 Hz it is 4 days, at 1.2 Hz it is 65 days. Powered by twin barrels. The tradeoff is lower accuracy at 1.2 Hz, meaning you will normally need to set the time after prolonged time at 1.2 Hz. Winding is done conventionally via the crown.