This alidade has an inverting telescope, striding level, vertical arc reading 30 degrees each way, and separate trough compass. It is part of a complete plane table outfit that Keuffel & Esser described "as made for the U.S. Coast and Geodetic Survey" and sold for $175. The Survey acquired this example in 1893. The inscriptions read “KEUFFEL & ESSER CO. NEW YORK CHICAGO 2447" and "U.S.C.&G.S. No. 91.”
Ref: Keuffel & Esser, Catalogue (New York, 1906), p. 408.
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