The CalUnitSystem (or Calibration Unit) is the ARGOS source used for AO calibration in day-time.
It creates 3 beams that mimics the 3 LGS beams: 532nm narrow band filter, same off-axis aberrations of M1 introduced using an hologram. It also provides an on-axis NGS source (actually a fiber in the ASM vertex re-imaged by the CalUnitSystem optics )
The optics are moved in the telescope's prime focus by a dedicated swing arm. The light is provided by 3 LED sources (for the off-axis beams) and a white source (for the on-axis beam)
It is developed and maintained by MPIA