I would like to mount a vintage scope on my single-shot Buffalo rifle. I have an old Fecker, but I don't know much about it.
1. Is there a way to determine it power?
2. What is the adjustable part in the center of the scope (number 0 -12)?
3. Can the date of manufacture be determined (SN 1556)?
4. Would it be eligible for scoped single-shot matches?

Dimensions are: 22" long, 1.27" objective, .91" ocular, .75" tube

I will attempt to answer some of your questions?  Feckers are generally nice scopes. John Unertl initially worked for Fecker before he went out on his own. 
I suggest you read Forum member's, Texas-Mac link.
It has some good info.
(You need to Login or Register to view media files and links)
1. Power is often marked on the knurled ring with the screws. This ring holds the reticle tube.  If it is not marked, determining the power becomes a judgement call. You must compare the scope again a scope of know power or estimate the magnification of an object viewed thru the scope. Best guess. Your scope would suggest a power between 4-8x maybe a 10 x but not much more.
2. The center portion ( knurled rings and index )  are the parallex adjustment which will vary for different distances ( 50yds- 100yds etc.) The setting must be determined by trial and error while looking thru the scope. You should focus the eye piece first on the reticle, before setting the parallex.  I can email you a copy of this brochure.  send me your email.
Kurt      

As I posted, one of my Fecker's took a 36" bath in Super Storm Sandy that was mounted on my CPA 32-40 barrel. Received the spanner wrench and started operating on the scope ... 

Questions for repairs:
1.  How many threaded sections are there to the tube?  Three or are there more?
2.  How is the sliding center erector lens removed from the middle of the tube? If there are not more than 3 threaded tube sections - would believe it is pushed to the front.  But installing it back in to the middle of the tube, lining up the 2 screw holes to the tube cut would be a feat of luck 
3.  If one of the reticle screws is broken off that means the cross hair wires cannot be replaced.  If I send the scope to one of the repair services, can they tap the screw out and put in new wires
4.  Should the lens be re-coated?
5.  The 2 front objective lens need to be glued back together.  Recommendations for type of glue to use?

Otherwise, I have the scope apart for cleaning.  When I removed the front lens, approximately an ounce of water poured our.  Was clear but Sandy left a black reside on the inside of the tube and on the lenses.  Bluing removed by the salt water needs a good touch up.

I truly believe this scope will be usable again.  Wish me luck!