Hi All,
Maybe this was answered already many times, but couldnt find an answer. This is rather a silly question but it is stuck in my head for some time already and I am seriously hoping you can help me close the topic

So here it is: does it wear off the power reserve more if you keep on chronometer on in the Speedmaster? Is that noticeable or neglectable? Or maybe it is a non existant issue?

 

The watch will stop sooner with the chrono running, but if you then disengage the chrono mechanism the watch will restart and will run to its full power reserve length.

 

My Apollo 11 50th ran for 55 hours with the chrono running. It didn't stop on its own, it was still running when I stopped the test. I'm curious how long it would run with no chrono running.

 

Around 64 hours.

 

Interesting, so we can assume that chrono can consume up to 20% of power reserve on condition that it would be running non-stop.

 

Sorry - more like 15%.

Thanks for the prompt feedback and my mind is at rest finally

 

The mainspring delvers a set amount of torque for most of the run time, and towards the end as the spring unwinds the level of torque drops off. As long as the frictional loads inside the watch are lower than the torque being supplied, the watch will continue to run.

There will be a point where the torque isn't enough to keep the watch running and it will stop. If you add a load to the watch, such as running the chronograph, the point where the load is too large will come sooner in the run time. So the watch hasn't used up more energy in that time, it just can't overcome the load - the same amount of torque is being supplied at say 50 hours from full wind no matter if the chronograph has been running all that time or not.

So when you run the chronograph and the watch stops, if you turn the chronograph off again, the load drops, and the watch is able to run again.

I recently did this test with a Cal. 1861 Speedmaster I serviced. I wound it fully, started the chronograph, and let it run until the watch stopped -that was 49 hours. I then turned the chronograph off, and the watch continued to run for another 2 hours before stopping, so 51 hours total. I then wound the watch and let it run down without using the chronograph at all, and it ran for 51 hours. This illustrates that the spring doesn't act like a fuel tank or battery...

 

Wow, thank you Archer - very informative! Although seems a little surprising to me that regardless of the load (with or without chrono) the torque will allow for exactly the same time. Maybe it is pure mechanics I don't understand or maybe the chrono is just insignificant in terms of how much more load it is? Only when little torque left then the watch stops sooner as you explained.

 

Maybe this will help illustrate - here is an example of a torque curve for a mainspring - vertical axis is the torque produced, and horizontal axis is the number of turns of the mainspring barrel:



If you run the chronograph or not, has no bearing on the torque curve of the mainspring. It will follow that curve regardless of the chronograph operating or not. What will change is the load on the movement, so the chronograph operating requires more torque to stay above the minimum required for the watch to run. Once that extra load is removed, the torque is now sufficient to allow the watch to run again.

You can perform the same experiment I did to prove this to yourself.

 

Thanks! All clear now!

 

Without the chronograph being switched on my Speedmaster Chronoscope is running for 68h. Switching the chronograph in it runs for 67h with a full wind. Its 9908 Movement has two barrels and is specified for 60h.

 

Thanks for the graph! Understandable!