PERPETUAL CALENDAR FORMULA

This book is the author's attempt at explaining how he came up with a mental system of the calendar (Julian and Gregorian) which was later converted into a tangible prototype. Also attached herein is the author's design for a two - dimensional perpetual calendar for both systems that can be used to check the veracity of one's mental calculations. Likewise, the process by which the codes were assigned or derived were also explained to establish the periodic cycles in both calendar systems. The rules for leap years for both systems were similarly discussed to illustrate the apparent difference between the Julian and Gregorian Calendar. Surprisingly, the Perpetual Calendar Formula itself only involves the operations addition and modulo seven if the final answer in not within the range of the Day Codes. Subtraction is only done for the dates in January and February of a leap year. The ultimate goal is to be able to make the computations mentally and it requires memorization of the Codes for Days, Dates, Months, Years and Centuries as well as performing the correct addition and modulo application. With constant practice and active memorization, one can emerge as a human perpetual calendar.