Methods and apparatus for service-level based andor skills-based assignment of a work item to one of a plurality of resources based on fitness, for example, of skills required by the former to those provided by the latter. The sidewall is extended from the bottom plate to define a receiving space. The light installer can minimize user interaction time by obtaining all necessary user authorizations early in the installation process, thereby enabling the light installer to install all components of the client-side application without further authorization from the user. A focusing light beam is projected onto the sample holder when the objective is located at the position, and the objective focuses the focusing light beam on the sample holder. In the drive shaft structure, the drive shaft includes a second surface located closer to the inner side of the radial direction than the outer peripheral surface, and the second surface includes an index mark used to confirm information on the rotation of the drive shaft or information on the displacement thereof in the axial direction.