A method and apparatus for routing a call to a subject matter expert via a packet network is described. The lower housing has arc gas emission holes formed in front and rear walls thereof, and is connected to a lower part of the intermediate housing via an engagement part such that the lower housing covers the lower part of the intermediate housing. A transmission member is mounted on the substrate for engaging the blade members, and a drive device drives the transmission member to rotate the blade members to open and close the optical path opening. In a first position, a first, smaller distance and in the second position, a second larger distance are provided between the bearing surface andor the lower edge of the clamping element and the contact surface of the respective distancing element is determined by the held shelf base. 4 ms, modulation m11 of a recorded signal when the recording light of approximately 780 nm in wavelength irradiates the recording layer via an optical system with NA=0. This prevents degassing of the additive from the electrolyte.