The photometric quality is derived from the extinction curve which is measured every minute. The sky is considered photometric when the extinction in V does not exceed 0.25 mag/airmass and the rms is below 0.025 for a reasonable time span. The light curve of a star near the pole supplies additional information about the sky quality.

It has to be taken into account that the field of view of the extinction monitor is limited to the northern part of the sky. Therefore it may occur that this part is clear while the southern sky is cloudy, although it is not probable that such a situation persists for a long time.

The Web Page displays continuously the following information:

• The operational status:
  • OFF means that the monitor is offline. This should occur only for maintenance.
  • STANDBY means that the monitor is operational but does not perform measurements (e.g. during daytime or in case of bad weather).
  • IDLE means that the monitor is performing measurements, but currently is in an idle phase.
  • ON means that the monitor takes data. This does not mean necessarily that an extinction coefficient is calculated. In case of bad conditions the coefficient is set to zero.
• The current extinction value, its rms error, and the relative intensity of a reference star, normalized to the hitherto measured intensity maximum.
• The extinction and its rms error as a function of time. (Click on the viewgraph in order to enlarge the timeline.)
• The intensity of the reference star as a function of time.