This compass belonged to John Johnson (1771-1841), the Surveyor-General of Vermont, and the American Commissioner for the survey of the boundary between Maine and Canada in 1817-1820. From correspondence in the John Johnson papers, now in the University of Vermont Library, we know that Johnson purchased several instruments from Richard Patten in New York. In March 1820, Johnson ordered two compasses, specifying in great detail which features he wanted on each. For himself he wanted a compass "of at least 7-inch Needle with a tangent Screw and Nonius as to turn it upon minutes." Johnson also ordered a $35 plain compass with a 6-inch needle, for a gentleman of his acquaintance.
The face of this compass reads clockwise. The vernier appears on a slit cut into the face, while the variation arc, which extends some 20 degrees either way, is located below. This vernier is moved by a rack and pinion on the north arm, and reads to 10 minutes.
Ref: Deborah J. Warner, "Richard Patten (1792-1865)," Rittenhouse 6 (1992): 57-63.
"John Johnson" in Abby M. Hemenway, ed., The Vermont Historical Gazeteer (Burlington, Vt., 1868), vol. 1, pp. 596-599
"John Johnson" in National Cyclopaedia of American History, vol. 17, pp. 290-291
Johnson's report on and correspondence relating to the Maine-Canada boundary survey, in University of Vermont Library.