An improvement is added to an optical time domain reflectometer for emitting pulsed light of invisible light to a measured optical fiber, receiving return light of the pulsed light by a light detection section, measuring the measured optical fiber, and emitting visible light for visible inspection of a fault point of the measured optical fiber to the measured optical fiber. The housing has a camming surface and the body is slidably connected to the housing. The conditions may include temperature gradients, concentration gradients of one or more compositions that quench etchant, pH gradients to assist in removing particles, andor concentration gradients of one or more compositions that assist in removing particles.