A combination of arc tool user interface features and operations are provided for efficiently defining an arc tool region of interest in a machine vision inspection system. Multiple distinct types of parameter control features are provide in an arc tool GUI. The distinct types of parameter control features may be distinguished by their relative locations, or by distinct symbols, or the like. One or more of the types of control features may include at least two modes of operation. In one such mode of operation restricted to one type of control feature, a user may change the nominal radius of curvature of the arc tool using a single cursor motion. In another such mode of operation shared by multiple types of control features, a user may rotate the region of interest of the arc tool using a single cursor motion.