Oka and uma

At the end of the game, the raw scores are converted into an "end game score". This is most commonly referred as the plus-minus (+/-) score. The four end game scores are always set up to sum to zero.

Oka and Uma

After the game ends, oka and uma are applied.

Oka

The oka 「オカ」 can be thought of as an "ante". When oka is used, all players pay a set amount at the start of the game. At the end of the game, the sum is given to first place. This sum is known as the oka.

The oka always is the difference between the starting score and target score. If the start score is 25,000 and the target score is 30,000, the difference would be 5k. Thus, every player would pay 5,000 points. Then, first place would receive (5,000 x 4) points back, for an oka of 20,000. Overall, first place gains 15,000 points and the others lose 5,000 points.

If oka is disabled, then even if a target score is set, no payments are made.

Uma

The uma 「ウマ」 is a set bonus/penalty for ending the game at a certain placement. The typical point spread uses the format of 「+A / +B / -B / -A」, where 1st place receives A, 2nd receives B, 3rd loses B, and 4th loses A.

The uma does not have to be symmetric. For example, uma can be set to 「+30 / -5 / -10 / -15」 or 「+15 / -5 / -5 / -5」. Uma usually adds up to 0, but technically does not have to. Modifications may be used to make the conditions easier or harder, namely in tournament settings.

Procedure

 
End game results with raw scores and uma scores

The end game score is calculated as follows:

  1. Take the raw scores from the end of the game.
  2. Subtract the target score from the final point values. (If no oka is used, subtract the starting score instead.)
  3. Find the oka and add it to the winner.
  4. Divide by 1,000.
  5. Round to the nearest integer. A result of 0.5 is rounded down, not up.
  6. Apply the uma spread.
  7. If, due to rounding, the sum of all four does not equal to zero, then the winner's score is adjusted to produce a zero sum. This adjustment is usually +/- 1 at most. (Note: in some rules, the loser's score may be adjusted instead.)

Formula:

End score = ((Raw points + Oka - Target)/1000) + Uma

Shortcut

For a given value of oka and uma, the overall change between raw score and final score will be the same. Therefore, by finding the net change from oka/uma once, you can skip having to do the entire process over and over.

  1. Before playing, calculate Final Score - (raw score / 1000) for each place. Use dummy numbers for raw score.
  2. After finishing the game, find the raw score, round it to the nearest 1,000 (rounding 500 down), then divide by 1,000.
  3. Use the calculated values from #1 to quickly determine final scores.

For example, if all players ended with 25,000 points, oka = 20k, and uma = 「+20 / +10 / -10 / -20」:

Raw score conversion Score comparison:
Uma 「20 / 10 / -10 / -20」
Raw scores Rounded to nearest 1000 Div by 1000 (A) End score (B) End score diff (B - A)
25000 25000 25 35 10
25000 25000 25 5 -20
25000 25000 25 -15 -40
25000 25000 25 -25 -50

This means, for these oka/uma settings, 1st place final score is equal to (rounded raw score/1000) + 10, 2nd place final score is equal to (rounded raw score/1000) - 20, and so on. In other words: instead of having to calculate oka and uma every single time, when you are 1st with these settings, you can divide score by 1000, then add 10.

Using the above picture as another example:

Raw score conversion Score comparison:
Uma 「20 / 10 / -10 / -20」
Raw scores Rounded to nearest 1000 Div by 1000 (A) End score (B) End score diff (B - A)
35700 36000 36 46 10
32400 32000 32 12 -20
22200 22000 22 -18 -40
9700 10000 10 -40 -50

First place received 35700 points, so their end score equals (36000) / 1000 + 10 = 46, which is what what first place actually got.

With different oka and uma

Naturally, with different oka and uma settings, the numbers will work themselves out differently than the 「+20 / +10 / -10 / -20」 set up.

With an uma of 「30 / 15 / -15 / -30」:

Raw score conversion Score comparison:
Uma 「30 / 15 / -15 / -30」
Raw scores Rounded to nearest 1000 Div by 1000 (A) End score (B) End score diff (B - A)
35700 36000 36 56 20
32400 32000 32 17 -15
30000 25000 25 -20 -45
9700 10000 10 -50 -60

Obviously, the net change is different.

Tie-breaker

 
End game results with two players with the same raw scores.

When scores are tied, there are two main variations to how it is handled:

  • Ties are broken based on the initial wind seating (seats in the first hand). When scores are tied, the initial East player beats South beats West beats North.
  • Tied players split oka/uma bonuses evenly. For example, with an uma of 「20 / 10 / -10 / -20」, if two players tie for 3rd, they would pay (-10 + -20) / 2 = -15 each.

Which variation is used will depend on the ruleset.

Competition formats

For some competitions, the same four players play out two or more hanchan to settle a score. This is due to one hanchan deemed as inadequate to settle a score between four players due to factors such as luck. Various tournaments and professional organizations utilize this format.

External links

Oka and uma in Japanese Wikipedia