Our current Gregorian calendar was introduced in October 1582 by Pope Gregory XIII as an adjustment to the Julian calendar, which was proposed by Julius Caesar and adopted on 1 AUC (founding of Rome) 709 (45 BC). Key to the change is the calculation of the date of Easter, which is the first Sunday after after the first full moon on or after the spring equinox. The adjustment added a leap year schedule and 10 extra days from Thursday 4 October 1582 to Friday 15 October 1582.
With (Steve) Hanke-(Richard Conn) Henry Permanent Calendar, every calendar date always falls on the same day of the week with a leap week added every five or six years. Also proposed is the abolition of time zones like China’s.