To make a calendar based on the numbering of weeks such as ISO week more interesting, the weeks can be labelled by playing cards rather than plain numbers.
In 1998, Karl Palmen thought of such a scheme. The 52 weeks of the years are divised into four seasons each represented by a suit: Clubs, Diamonds, Hearts and Spades in that order with a joker for the 53rd week in any year it occurs. The weeks within each season are labelled Ace, Two ...., Ten, Jack, Queen, King.
If the ISO weeks are used the deck is referred to as the ISO deck. Similarly, when applied to any other week numbering scheme, the deck takes the name of the scheme.


The Medieval LuniSolar Calendar Edit
The Medieval LuniSolar calendar is invented by David B. Kelley.
Suit  Gender  Season  Life Cycle  First Day of Season  Middle Day of Season  Last Day of Season 
♥  ♀  Spring  Infant  Feb. 1 (Imbolc)  Mar. 18 (Ostara)  May 2 
♣  ♂  Summer  Young  May 3 (Beltane)  June 17 (Midsummer)  August 1 
♦  ♀  Autumn  Adult  Aug. 2 (Lughnasadh)  Sept. 16 (Mabon)  October 31 
♠  ♂  Winter  Old  Nov. 1 (Samhain)  Dec. 16 (Yule)  January 30 
*  ♂  Black Joker  January 31  Leap day actually falls
between Feb. 24 and 25.  
*  ♀  Red Joker  February 29 (in leap years) 
The Julian calendar year was 11.2334 minutes short of one solar year. This caused the equinoxes and solstices to drift, calendrically, relative to their 325 AD dates of occurrence. To solve this problem, the old Julian calendar ended on October 4, 1582 and the very next day was called October 15, thus beginning the Gregorian calendar. The 'Playing Card' calendar shown on this article may have been made during the period when the spring equinox fell on or near March 18, ie. around 709 AD.
Drift of the spring equinox in the Julian calendar after the counsil of Nicea in 325 ADEdit
 in 325 AD, March 21
 in 453 AD, March 20
 in 581 AD, March 19
 in 709 AD, March 18
 in 837 AD, March 17
 in 965 AD, March 16
 in 1093 AD, March 15
 in 1221 AD, March 14
 in 1349 AD, March 13
 in 1477 AD, March 12
Lunar calendar aspects Edit
A♥  5♥  9♥  K♥  4♣  9♣  K♣  4♦  8♦  Q♦  4♠  8♠ 
Q♠  3♥  7♥  Q♥  3♣  7♣  J♣  2♦  7♦  J♦  2♠  6♠ 
10♠  2♥  6♥  10♥  A♣  5♣  10♣  A♦  5♦  9♦  K♦  5♠ 
9♠  K♠  4♥  8♥  K♥  4♣  8♣  Q♣  3♦  8♦  Q♦  3♠ 
7♠  J♠  3♥  7♥  J♥  2♣  6♣  J♣  2♦  6♦  10♦  A♠ 
Starting with the A♥, and proceeding clockwise, the wheel of cards becomes a very effective predictor of lunations (accurate to within one week), if one uses the following simple formula: +4 cards (5♥), +4 cards (9♥), +4 cards (K♥), +4 cards (4♣), +5 cards (9♣), and then the sequence with the same number of added cards (ie. +4, +4, +4, +4, and +5 cards). By following this formula, one finds that all 52 cards are eventually selected, as well as six cards which are repeated; thus, a total of 60 cards /lunations are specified, as shown above. The shaded cards indicate which those are repeated. In order to test how closely the predicted cards agree with reality, I tracked the occurrences of New Moons, starting on February 1, 1919 (JD 2421991), through a sequence of 60 lunations, ending on December 8, 1923 (JD 2423762, or 6♠). Of those specified by the card sequence, only six disagreed with the actual occurrences (the 8♠ and 7♦ were each one week too late, and the 3♦, J♠, 6♣, and A♠ were each one week too early). Assuming that the first lunation occurred just after the start of the first day (ie. at JD 2421991), if one adds 1771.835 days (ie. 60 × 29.53058867 days), one would expect that a full round of 60 lunations would be complete at 2423762.83532  which it does. Thus, it appears that the card calendar may have been designed to go through a sequence of 253 complete weeks (1771 days/7 days per week), starting with the first day of week is 7.003302 days (ie. 1771.8353202/253 weeks). And, given that the number of days per cycle amounts to 1771.8353202 days, then, if that figure is rounded off to the nearest whole day, we arrive at a final figure of exactly 1772 days per cycle, or an average of 29.53333333 days per lunation (ie. 1772/60), which is, indeed, quite close to the actual figure of 29.53058867 days per lunation. Finally, one perhaps cannot but feel that the calendar wheel is also connected with the Metonic cycle, because if one goes beyond the 60 cards shown above, to the 236th card in sequence, one reaches the K♠ (and the date January 31, 1938, or JD 2428930, in the actual lunation tracking). And so, from February 1, 1919, which could be considered the first day the A♥, until January 31, 1938, which could be the last, and eighth, day of the K♠ (or the black Joker), the total number of days amounts to 6939 days (ie. JD 2428930  JD 2421991), or 234.9767 lunations, or one complete Metonic cycle.