Horace Minot Pool (1803-1878) began working with his older brother John in the mid-1820s, making a variety of mathematical instruments. In 1841, when John withdrew from the firm, H.M. Pool continued on his own. The 1860 Federal Census of Industry reports that, with the help of six male hands, Pool had an annual production rate of 55 compasses worth $1650, 18 transits worth $1800, 2 theodolites worth $550, and miscellaneous items worth another $500. Pool showed two "circumferentors" at the Massachusetts Charitable Mechanic Association fair of 1850, and his surveying instruments won a silver medal at that association's fair in 1874.
This compass, which belonged to Colby College, has a variation arc on the south arm that extends 15 degrees either way; the vernier is moved by a tangent screw, also on the south arm, and reads to 4 minutes. There are two level vials on the north arm.
Ref: Donald and Anne Wing, "The Pool Family of Easton, Massachusetts," Rittenhouse 4 (1990): 118-126.