Photometric analysis of the Pi of the Sky data.

Accurate analysis of Pi of the Sky data is very important because of a number of factors that can influence measurements. Reading the chip with the shutter opened, strong and varying sky background, passing planets or planetoids, clouds and hot pixels are among possible sources of errors in our measurements. In order to facilitate analysis of variable stars we have developed a system of dedicated filters to remove bad measurements or frames. The spectral sensitivity of the detector is taken into account by appropriate corrections based on the spectral type of reference stars. This process is illustrated by the analysis of the BG Ind system where we have been able to reduce the systematic uncertainty to about 0.013 magnitudo. We also try to take into account the statistical properties of the whole frame. Obtained results allow us to reduce errors twice.