The Pi of the Sky is a system of two wide field of view robotic telescopes, which search for short timescale astrophysical phenomena, especially for prompt optical GRB emission. The system was designed for autonomous operation, monitoring a large fraction of the sky with 12m - 13m range and time resolution of the order of 1 - 10 seconds. Two fully automatic Pi of the Sky detectors located in Spain (INTA) and Chile (SPDA) almost every night have been observing the sky in search of rare optical phenomena but also collect a lot of usefull observations which include e.g. many kinds of variable stars. To be able to draw proper conclusions from the data received, their adequate quality is very important. Data of the Pi of the Sky are subject to a systematic errors caused by various factors such as e.g. cloud cover seen as significant fluctuations in the number of stars observed by the detector, the problems with conducting mounting, a strong background of the moon or passing of a bright object near the observed star, such as a planet. Some of these adverse effects are already detected during the cataloging of individual measurements, but the quality of our data was still not satisfactory for us. In order to improve quality of our data we developed two new procedures which were based on two different approaches. In this article we will tell some words about these procedures, give an some examples and show how these procedures improve the quality of our data.