Used immediately. The handy size and shape of the pen fits perfectly in your pocket. It won't work right away, but I think it was my own fault for not screwing it in tight enough after installing the batteries. Once installed, it connects to both ends of the larger fiber optic jumper. I mainly use the SC connector as I have adapter cables that fit most other connectors. An incredibly bright red light worked to identify the other end. Highly recommended as an inexpensive VFL.
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