A true power reserve indication without setting
Power reserve indicators were found in most of the highgrade timepieces. One reason for this was that one should wind them preferably at the same of the day, daily. This ensured that they most likely run under the same conditions. Day after day, week after week, month after month. If one forgot to wind it one could read it on the power reserve display. It was not necessary to wind it just to be on the safe side. This namely would have a negative impact on the rate of the watch.
All of this ‚oldtimers' had one feature in common: There was a defined ‚ fully wound status', but also a defined ‚run out state'. Be it the fusee in the chronometers or the setting in mainspring watches.
But today's watches don't feature this - for good reason: a setting only bears risks; and even stops the watch if it does not work properly.
The absence of a defined zero-point in modern watches makes it difficult to construct a power reserve indication. A friction coupling is an often used solution which masks this drawback.
With the VA it is quite different. Here no friction coupling is necessary because we have a defined zero point. But not achieved by a setting, but up to date by a second's stop, which engages precisely after 40 hours. You can study the function by looking at the picture above. The cam disc at the right figure part turns for 240° once in 40 hours. During this a lever of the switching ring is gauging the position of the cam disc and transports this information via a gear segment and a pinion to the power reserve indication. After the 40 hours have past the switching ring additionally operates a lever that stops the seconds hand (left part of the figure).
This mechanism is unique. It combines the virtues of the ancients with the needs of today.