The article investigates the origin of P. V. Khavsky’s passionate devotion to chronology. Khavsky was a professional lawyer and a senior official in the middle of the XIX century. He studied the Russian chronology, especially one of its areas, such as Easter time calculation system. Much attention is given to Khavsky’s merits in this branch of knowledge. It is noted that he was first who tried to explore the Russian Easter time historically. He tried not only to present the summary of the Easter terms but also to study the history of their use in Russia. P. V. Khavsky formed his own view of the Russian Easter system that allowed him to get closer to important scientific discoveries. In addition, Khavsky was the first to discover the sources of calendar styles, in which the year of March was 6 months ahead of the September one. The article emphasizes the fact that the assumption was to bring then contemporary historians to the conclusion that the sources noted variable position of March year in comparison to the September one, namely with it semi-annually keeping ahead and semi-annually lagging behind. But that conclusion did not fit in then dominating development scheme of the old Russian time calculation, which was reduced to the idea of applying a landmark calendar style. Therefore, Khavsky’s most important discovery was rejected by most contemporary researchers.