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Many thanks Bob - the photos are very helpful.  If I can trouble you with a follow up question, is the entire black piece on top of the bearing cover in the third photo the washer we see in the first two photos?  Or is there more than one washer?  The washer doesn't look as thick in the first two photos, but maybe it's just the angle?

Best of luck with your restoration.  I was fortunate other than this one missing part - the mirrors and scope are all very good, the paint is pretty good, and once the old caked on grease was cleaned off and replaced it seems to work well (though I haven't adjusted the mirrors or shot any sights yet).  The arc was quite badly corroded as well as many of the screws, but they all cleaned up nicely.  Also had corroded batteries in the handle, but managed to get them out and get the lighting working.  

Would you happen to know the difference between the sextant number on the certificate (and the arc) and the serial number on the certificate (which I haven't noticed anywhere on the sextant)?  I also see we have different "book" numbers - not sure what that is.  Mine has a Swedish importer's name imprinted on the index arm - maybe that has something to do with it.

Once again, many thanks for the photos.

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