This alidade belonged to Columbia University. Its vertical arc, which extends 35 degrees either way, is graduated to 30 minutes and read by vernier to 2 minutes. The base has a skeletal structure, making it light and stiff. There is a separate striding level and trough compass. The "BUFF & BERGER BOSTON 2157" inscription refers to a firm that traded, as such, from 1871 to 1898.
Ref: Buff & Berger, Hand-Book and Illustrated Catalogue of the Engineers' and Surveyors' Instruments (Boston, 1890), p. 104b.