This is a stupid question I now but it has been vexing me for a while now.
So, would a watch run better in a vacuum? Does air resistance have any affect on the balance? If air resistance did have any effect on the swing of the balance wouldn't it keep time better, but the effect may be so minute it would not effect the time keeping abilities.
It is a trivial question, but interesting all the same.

Also here is nice video I found on a watch with improved aerodynamics (the balance).
http://www.youtube.com/watch?v=qjx6lxJl78Q

Francesco

Francesco, not a stupid question. Air resistance does have an effect on the balance. Here is an interesting video on the Cartier ID Two concept (wrist) watch where they have incorporated many improvements to increase efficiency. One of these is drawing a vacuum on the inside of the case which they say makes a substantial reduction in the amount of energy required to operate the balance.

cartier ID Two

Thanks Robert great video.
But I just realized, you wont be able to hear the watch

Francesco,
Answer #1, Please refrain from demeaning yourself with "stupid". We all admire your strength of intellect, character and courage to deal with us at all.

2, Vacuums are relative and as watches are lubricated with oils which will evaporate in a "hard" vacuum the question is somewhat academic.

Many years ago, I worked with a couple guys at Fafnir Bearing (when "made in USA" still had meaning) to resolve the problem with precision bearings in space "freezing" becuase they actually were welding together when in a vacuum (super-finished steel does that).

We resolved the issue with Sapphire Balls or rollers instead of steel. Then the bearings did not freeze up in space. Today, I would use my favorite material Zirconium Oxide, but then we had not learned enough.

With watches, the "free spin" testing that requires the balance wheel freely oscillates on its pivots for at least 30 seconds before final assembly has always fascinated me due to the apparent absence of significant air friction. In a vacuum it may run longer, but there is also the internal friction of the hairspring which converts some compression and extension to a few ergs of heat may well be a similar order of magnitude as air friction.

Francesco that is a great question. I see many tire companies advertizing nitrogen filled tires and that started me wondering if a nitrogen filled watch would work differently. See you are not the only stupid thinker!

Deacon, doesn't nitrogen make the tires squeaky sounding like when you breath "laughing gas'? Actually Nitrogen is inert and hence less reactive to tire rubber. It also (is reputed to) hold pressure better with temperature. It is nearly the same atomic weight(7) as Oxygen(8).

Mebbe the watch will not rust with Nitrogen in it, but how do you seal that? You have a couple Nitrogen filled scopes to eliminate condensates.