Jassen

Jassen is a game for four players. This version is Differenzler, a variant of Jassen. Each player plays alone, there are no teams. The object of the game, for each player, is to predict the number of points s/he will have in the tricks s/he wins as accurately as possible, at the beginning of each round. The difference between this estimate and the actual points are counted as negative points.
There are 36 cards used in the game (four suits of nine cards each). Each card has its own value, which, with the exception of the 10, is more or less equal to its strength in a trick. The values are as follows: 

If a suit is a trump this changes the strength and value of the Jack and 9. trump Jack is worth 20 points and a trump 9 is worth 14. The values of the other trump cards remain the same. 

Game
A Game is played for four rounds. The First Hand (the first to play) is chosen at random, and players take turns being the First Hand in each round.
At the start of the game each player receives nine cards face-down. The last card of the player who deals decides which suit is trumps. All players can now look at their cards and call a number between 0 and 157, as estimates of possible points. A player can either announce this to the other players, or keep it secret.
The First Hand is always the first to play. Whoever wins a trick starts next. Points are counted up once all nine cards have been played.

Game over
Points are counted up at the end of each game. All players count up the points of the cards in their respective tricks. The „Weisen“ and „Stöcke“ in other variants of Jassen do not count in Differenzler Jassen, only the difference between the estimated and actual number of points is counted as negative. The player who wins the last trick gets five bonus points. After four rounds (a full game) the negative points of all players are added. The player with the fewest negative points wins the game. In case of a draw, an additional round is played in order to determine the winner.

Playing Cards and Winnings Tricks
Any card can be played, in accordance with the following rules:
If a player has a trump card, it has to be played, with the exception of the Jack. Otherwise a player can play any card s/he wishes.
If a player does not have a card of the suit played, s/he is free to play any card. If a player has a card of that suit, s/he has to play it, or else a trump which is higher than the others played until that point in the trick.
The highest trump card wins a trick. If there was no trump, the highest card of the suit played wins. In Differenzler Jassen players are allowed to look at their own tricks and count up the points for them.