Penchan

A penchan machi is a type of machi, i.e., a wait shape of a tenpai hand.

A penchan machi contains the tiles 1 and 2 of the same suit, or 8 and 9 of the same suit, waiting for the completion of the shuntsu with a 3 or 7.

, winning tile:

Penchan is often used for a 1-2 or 8-9 shape within the hand, even while the entire hand has not reached tenpai.

Fu

Because the winning tile does not complete a shuntsu which was completable on two sides, winning from a penchan awards 2 fu to the hand and does not count as pinfu. Sometimes, a winning tile can be interpreted to complete either a penchan or something else, and the higher-scoring interpretation will be used.

, winning tiles: or

This hand qualifies for pinfu on both winning tiles. If a 3-pin is used, it is interpreted as completing the ryanmen 4-5 with the shuntsu 1-2-3 already in place.

, tsumo:

This hand, however, will interpret the 3-pin to complete the penchan 1-2 instead of the ryanmen 4-5. It doesn't qualify for pinfu anyway because of the 1-sou ankou. This interpretation makes the hand worth 40 fu instead of 30: It has 20 base fu, 8 fu from the ankou, 2 fu for winning by tsumo, 2 fu for the penchan machi, making 32 fu in all, rounded to 40.

Strategy

Penchans are bad shapes. Only one tile will immediately make a shuntsu. It is very hard to develop them otherwise: For a 1-2 penchan, the 4 of the same suit is a useful tile, on which the 1 may be discarded. A 2-4 shape can be completed with only one tile still, or turned into the ryanmen 4-5 by drawing the 5 and possibly discarding the 2.