This calander is based on the Aitken Perpetual Calendar (Robert G. Aitken, Director Emeritus of Lick Observatory)

Some brief notes on the Martian calendar:

The length of a Martian day, in terrestrial time, is 24 hours 37 minutes and a pocketful of seconds.

Martian years come in three flavors: (1) 668 days in length, (2) 669 days in length, (3) 670 days in length. This works out pretty well as it allows the Martian calendar to be perpetual on a two-year basis.

Odd-numbered years are always 668 days in length. Even-numbered years are always 669 days in length. A leap-day, called Mid-Year Day, is inserted every ten (Decennial) years into the 4th Quarter of Summer to counteract a one-tenth of a day per year variance. As this is an even-numbered year: 669+1 = 670 days in length. (Why isn't it this easy on Earth?) This procedure will keep the Martian calendar accurate for ten-thousand years into the future.

The Martian year is divided into quarters, as on Earth, but begins with the Vernal Equinox. Each quarter (Spring, Summer, Autumn, Winter) is sub-divided into quarters as well.