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NGC 6690 = NGC 6689. Both Swift and d'A found this galaxy twice. D'A, however, realized that his two observations refered to the same object, while Swift's second position was far enough off to mislead him into including the galaxy twice in his fifth list. Dreyer somehow recognized Swift's mistake, so only included one of the entries in NGC -- but he (Dreyer) also missed the identity with d'A's object, even though the two positions are less than an arcmin apart on the sky.
Whatever happened, there is certainly only one galaxy, and it clearly bears two NGC numbers. The several descriptions are good, and all the nearby field stars are just where d'A and Swift put them in their notes.
The RNGC (Sulentic and Tifft 1973) notes that this is a 12.5 mag galaxy. Their coded description reads EON,BM,SLDIF,EQDKLN.
The Messier objects
The Bennett objects
The Caldwell list
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