website\
<http://astro.univie.ac.at/en/institute/light-pollution/>.

A tool is provided for calculating all relevant information about illuminated moon fraction, moon rise, moon set and dates for civil, nautical and astronomical twilights. Furthermore we calculate mean, best and worst values as well as statistical information for the defined time intervals (e.g. nautical twilight). Some other values like the “naked eye limiting magnitude” or the “clear sky factor” are calculated, but still in an experimental phase. A future discussion on that is planned.

### Intercomparison and relative metering precision of our two SQMs

For checking the quality of the photometric data, we have made a parallel measurement with our two devices “IFA” and “FOA2” over a period of 33 days. Since an absolute calibration to any given standard such as Johnson V seems to be difficult for the moment, the question to be answered was, weather both of our devices give similar response under the same environmental conditions. Therefore, the devices were installed at exactly the same place at our institute and pointed to the zenithal region of the sky. The daily comparative light curves observed can be found in the appendix (Figs. \[fig:qualitylightcurves1\] to \[fig:qualitylightcurves3\]).

Analysis of the data showed that for the substantial fraction 