In 1136, the 26-year-old Novgorodian Kirik wrote a scientific treatise on time counting units, the basic concepts of the calendar and the use of this information in chronology. The Old Russian author demonstrates a high ability to count, making accurate calculations with numbers of the order of tens of millions. This work characterizes Kirik as the founder of the application of accurate methods in Russian science. This book is written on the basis of the texts of Kirik's work using the works of domestic and foreign authors.