A conditioning bottom has a main body and a strong tightening portion which is in the form of a belt and has a tightening force stronger than a tightening force of the main body. 6 \u03bcm fluorescence emitted from Ho3+:5I5\u21925I7 transition as an optical amplifier, and an assistant pump wavelength band capable of accomplishing population inversion between 5I5 level and 5I7 level to improve the signal gain characteristics of such amplifier. A port that, by queuing a message descriptor to the transmit queue of a destination port, causes the number of message descriptors queued to the transmit queue of a destination port to equal or exceed its high threshold, is flow controlled by the destination port. Accordingly, although the optical sensors each react to the reflected light from the photopolymer plate, the optical sensor does not react to the reflected light from the interleaf paper. Embodiments of the present invention will simplify and accelerate accurate measurements of free chlorine in water, without interference from compounds impacting present measurements of free chlorine.