A method for manufacturing a glass rod, which is a parent material of an optical fiber, comprising: adjusting a vertical inclination of a standard rod having a predetermined straightness; and heating and elongating a base material, which is a parent material of the glass rod, along an axis of the standard rod, the vertical inclination of which is adjusted, to generate the glass rod. The mirror chamber has an oval longitudinal section, and is provided at an inside thereof with a mirror. Location data is accessed that identifies one or more locations associated with the user. A comparator integrates the various frequencies and compares them to a threshold signal.