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I'm curious about this and interested in both anecdotal evidence and hard numbers if available.

My anecdotal evidence:
My ETA autos that I've had seemed to wind with regular wear with no trouble, my Seiko 7S26 models seemed to wind slightly better.

The Orient auto I got a few days ago has an RDM display. I remember reading somewhere that their autos are known for being very efficient winders. I have been amazed at how little wear and movement it takes to push that RDM needle right up to 40 hours. Of course I've never had another auto watch w/ an RDM display to compare, but the Orient does seem VERY efficient.

I realize this also gets into bi-directional vs. uni-directional winding discussions. Anyone have info to share on the topic?

Thanks!!
 

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Any bidriectional system probably has the same "efficiency", in that the ratio of (work added to the system by your movement) over (work applied to the mainspring) is nearly the same.

The Seiko "magic finger" (or whatever they call it) designs add power reserve faster, but require more torque, the Eterna system (used by ETA) is geared down so the torque requirements are lower but more revolutions of the rotor are required to wind the spring.

Obviously, anything that winds in both directions will be more efficient than than anything that only winds in one direction. And further, anything that fully rotates will be more efficient than anything that must stop and return to complete a cycle (i.e., bumpers).

All that being said, bumpers, which we can all agree are the least efficient system out there, are capable of keeping a watch wound under normal activity, so the whole question is kind of moot.
 

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The Seiko "magic finger" (or whatever they call it) designs add power reserve faster, but require more torque, the Eterna system (used by ETA) is geared down so the torque requirements are lower but more revolutions of the rotor are required to wind the spring.
Thanks to lysander now I know why my 7S26 rotor is somewhat resistant to movement, especially when the power reserve is apparently near the max.
 
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