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A. Lange & Söhne

It's a freesprung system....

 

Hi,
it's a freesprung hairspring, i.e. the actual length is fixed. Different from the commonly used systems, where the hairsrping end is either glued, laser welded or fixed with a conical pin to the hairspring stud - the Lange system is a sort of clamp, fixing the hairspring with help of two "rounded jaws" (hope this isn't a misleading term). 
This clamp system is movable, which is guided by the index with swan neck/micrometer screw. This regulation only changes symmetry of beat - not the rate.
The actual rate is adjusted firstly by the actual length of the hairspring (rough pre adjustement), fine adjustement is done through the variable inertia weights on the balance rim. Of course any change to the clamping point/length asks for a re-adjustement of beat symetry (i.e. same length of the tic and tac ;-)  ).

Having a fine adjusting micrometer/swan neck for the symetry of beat isn't necessary IMHO, but of course looks nice and of course the swan neck is used as a trademark for any precision movement for long time.

Hope this isn't explained too confusing though.
Best regards
Suitbert

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