In 1834 Mastrofini offered to create for the world an "eternal" calendar, and demonstrated that its invariance can be achieved only by application of special days that would not belong to any week or month. He offered to establish a calendar year of 364 days, always beginning on a Sunday, split into 52 seven-day weeks, and to place the 365th day of each year at the end of December, considering it "extra-calendrical," special, or out of week.
He planned one more special intercalary day in a leap year, and to place it in the middle of a year, between the last day of June and the first day of July, or following the first special day.
