An apparatus for use on a surface and responsive to an operator. A head assembly is adapted to carry a device for engaging the surface. An actuator raises and lowers the head assembly relative to the surface. A position control responsive to operator input indicates a head position of the device relative to the surface or range of head positions of the device relative to the surface. The head position or the range of head positions indicates a distance or range of distances, respectively, between the device and the surface. A controller responsive to the position control selectively actuates the actuator to maintain the device in the head position or within the range of head positions as indicated by the position control. As a result, a repeatable position or range of positions of the brush head is obtained, the relative engagement between the head assembly and surface is controlled and the treatment of the surface by the head assembly is controlled. Position control may be used in combination with torque control of motors driving brushes for engaging the surface.