Questions about the measurement of quantities (about named numbers) make up a significant part of the arithmetic course of primary school. The student should get acquainted with these issues not only in the classroom, but also by reading books available to him. To provide this opportunity, a real book is published in the Schoolboy Library series. She presents an updated edition of the book "Measures and the Metric System" by the same author for children (Detizdat, Leningrad, 1953), awarded a prize at the competition of a popular science book for children (1954-1955). Please send all comments and wishes to the address: Moscow, Chistye Prudy, 6. Uchpedgiz, editors of mathematics.