In 1929, the government of the U.S.S.R. decided to reform the Gregorian calendar, which was in use. A five-day week was created, in which there were four working days and one day of rest. A month was made up of six weeks. The five or six intercalary days were holidays. The days were numbered, but the names of the months were not changed.
In 1932, the number of weeks in a month changed to five; and the new six-day week had five working days. This was not popular. In 1940, there was a return to the Gregorian calendar.