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What theoretical advantage, if any, does a duo-in-uno hairspring possess over a helical hairspring?

Incroyable

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Jun 26, 2022
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I have an interesting duo-in-uno watch.
Unfortunately an orphan, and in terrible condition.
Fascinating though.
Negus Brothers #5688. From around 1884, I believe.

All of the steel components have an interesting black finish that I've not seen before.
The screws, springs, all the motion work, the balance wheel and the spring, even the pinions and arbors have this peculiar black finish.
Looks like it was all powder coated or something.

The hairspring is very distorted, sadly. What has always caught my attention, besides the duo-in-uno, was that the spring is very thick. Almost square stock.

Regards,
Steven

View attachment 738472 View attachment 738473 View attachment 738474 View attachment 738475
Would this have been made for this specific Negus Brothers?

 
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Dr. Jon

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Most of the duo-in-uno sprung watches I have seen are also by Walsh but sold by Sam Hammond also of New York.
 

Incroyable

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There was apparently an OF Parkinson & Frodsham duo-in-uno in its original gold case that sold last week at a local English auction.

A watchmaker acquaintance sent me some photos of it after the fact.
 

Dr. Jon

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Also likely made by A. P. Walsh. The firm submitted two Walsh watches to the 1876 Geneva open regulating competition which listed as regulated by Walsh.
 

Bernhard J.

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What is thought about triple overcoil hairsprings? Is that sort of a duo-in-uno with a shorter helical part?

Cheers, Bernhard
 

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