When you forget to wind your manual speedy and it runs out of juice:

(a) does it simply stop, or is there a period in between where it runs more slowly and gradually comes to a halt

(b) if there is a period where it starts running more slowly just before it is going to stop:

(i) how long does that period last for; and
(ii) is the chronograph function affected, ie will the watch be less responsive to start/stop/reset of chronograph etc.

I'm assuming the answer is the same for calibres 321, 861, 1861...

 

Timekeeping may change as the spring runs down, but whether it goes faster or slower depends on various things...

The length of time when timekeeping will be affected will vary with the condition of the watch. The power reserve is not affected by the chronograph being on, however the watch will stop sooner since the added tourque needed to run the chronograph parts may be more than the mainspring is delivering when it's close to being stopped...

Cheers, Al

 

Thanks both - fascinating and as always amazing depth of knowledge you guys have!

 

Is that true? Fascinating. I'll test it immediately (that is to say: once my fully around 861 rubs out of juice).

It's quite counterintuitive. You'd think that since the chronograph requires energy, it'd run out sooner. If not, where does the 'extra' energy go when the chronograph isn't running?

 

Springs don't work like batteries as far as how much power they transmit. Elastic energy is different from electric energy.

Each "tick" of a watch lets the spring move a small amount. The spring doesn't change total length ever. It doesn't move faster or move in larger intervals when the chronograph is running.

 

Mine runs a little quicker after 24hrs. I usually wind it every day but if it's running a little slow I might wait and wind on the 2nd day (before it stops of course) to aid a little bit of timekeeping.

 

Stop thinking of it as energy and think of it as torque. If the torque being delivered by the mainspring is larger then the torque required to make the watch run, the watch will run. If the torque from the mainspring is below the threshold level required to make the watch run, it no longer runs.

So there are 2 things that can be in play here. One is that the amount of torque from the mainspring can drop, and the other is that the threshold torque required to make the watch run can go up. The rate that torque is reduced from the mainspring really doesn't change much - the spring would have to get weaker somehow for that to happen. But the threshold required to keep the watch running can go up through added loads. That can be from a date change complication, from adding in the parts to run a chronograph, or just from the watch getting dirty over the years.

Raising that threshold doesn't decrease the torque from the mainspring. The torque is still there, it's just not enough to make the watch run. Try fully winding your watch, turning the chronograph on, and let it run until it stops. Then without winding again, turn the chronograph off and see how long the watch continues to run...

If I use my index finger to push on an empty chair with wheels, I can move the chair easily. If there is a 300 pound guy sitting in that chair, and I push with the same force as before, the chair won't move. The chair (or feather, or building) has no impact on the force I apply with my finger, only if that force is enough to move the object...

Cheers, Al