@glens
Those are standard Winchester Carbine Ladder Rear Sights and are the correct sights for an 1892 model Winchester rifle.
https://www.google.co.nz/?gfe_rd=cr&...+ladder+sights
The ladder sights were also an option when ordering your rifle and I believe they stopped using this sight for 1892 rifles in the early 1930's so this may also give a clue to the age of your rifle.
My 1892 Winchester has the Semi Buckhorn Rear Sights which was also a "Option" you could choose when you ordered a Rifle.
You could also order Full Buckhorn rear sights, as well as the Tang sights and a range of different fore sights in differing heights.
I'm not sure about the graduations on the ladder but as they are an equal distance apart they might not be denoting yards.
Might have to research this some more though.
In the meantime here's a good article on the history of the 1892 Winchester Rifle
http://outlawswinchesters.jouwweb.nl/winchester-1892
Cheers
Pete
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