Leap year and the Gregorian Calendar

2016 is a "Leap Year". That means we will also vote for President. The concept of having a Leap Year every four years was introduced by Julius Caesar in 46 BC and assumed that the year was 365.25 days long.  After a few hundred years, that error began creeping up and in 1582, Pope Gregory XIII introduced the modified Gregorian Calendar widely used today. It corrected the length of a year to 365.2425 days using this clever algorithm:

Every year that is exactly divisible by four is a leap year, except for years that are exactly divisible by 100, but these centurial years are leap years if they are exactly divisible by 400. For example, the years 1700, 1800, and 1900 are not leap years, but the years 1600 and 2000 are.