Every few days, young boys and girls walk into the office with their parents. "My child is a genius/prodigy, you ask him any date of any year and he/she will tell you the day. Tell him/her your date of birth and he/she will tell you the day on which you were born," says the mother/father.Well everyone can be this calendar genius. It doesn't even require mathematical knowledge or number crunching. It involves memorising a few nifty tricks and using a bit of logic. The basic law is that the first day of any year can begin only one of the seven ways. So, there are seven calendars that can be shuffled in innumerable ways depending on the seven ways in which the year can end. So start off with making seven calendars, which begin on one day of the week and have 28 days in February, as we all know the number of days in other months stay constant. Label the calendars A, B, C, D, E, F and G create a mental picture of these calendars. Ah! Didn't we consider February that unleashes a Leap Year and throws the calculations askew? Simple, in the combination of seven calendars, just shuffle the calendar to the next one from March you have factored in the 29-day February. Is that all? No. The Leap Years occur in a pattern and have to be divisible by four. Once all these issues are factored in, you have the perpetual calendar. And call yourself a genius/prodigy.