A grease gun with a rotary oil injection tube comprises an oil storage tank, a valve seat, an oil injection tube and a press rod. Expansion handles may also be displayed adjacent nodes in the tree diagram. The perfusion branch comprises a self-sealing component, that after predetermined period of time precludes fluid flow out of the distal end of the perfusion branch. Thus, a signal output from the error signal detecting apparatus does not change when a shift is generated in the objective lens or the distance between the objective lens and the disc is deviated from the on-focus position.