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Adolf Gustav Ditscheiner1846-1904
Regarding the value of your item, I have just perform a market research of similar sold items as yours. I performed the research based upon the most recent finished auctions and private sells, so the value given is the real market value of your item. This is the only way to know the exact value of your unit.
The value will be in the range of 4,000-5,000$.
I would recommend to sell your unit through a direct sell, but in your case it would be much better to sell through a big auction house. I would contact both Christies, Bonhams or Sothebys, they have a good record on past auction sales of Adolf Gustav Ditscheiner. You will have o pay the auction house fee, around a 20-30% of the final auction price, but it will be worth it. For example, this piece was appraiser in 2,000-3,000, but the final price got more than 6,000:
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