Comments:
A split, bimetallic balance
NJ's post of a beautiful calibre 454 inspired me to post a detail from a photo of a pocket watch Calibre 439 from 1949:
Bill
Bill
Gorgeous, thanks Bill
such a wonderful movement and a workhorse for V&C pocket watches. A few hundred were made with aluminum plates and bridges:
Calibre V439
Vacheron & Constantin Deck Chronometer
And then we have this beauty ...lifted from SteveG's Watch Launchpad ...
Great shot Bill
I have somewhat lost my first love which is for VC but you guys on this forum are keeping the flame alive for me! 
Cheers
Robin
Cheers
Robin