Penchan
A penchan machi is a common type of machi. This machi contains the tiles 1 and 2 of the same suit, or 8 and 9 of the same suit. The pattern is limited to waiting for the completion of the shuntsu with a 3 or 7. At maximum, only four tiles are available for completion.
Pattern
, 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. If it were interpreted as a 1-2 penchan winning with 3-pin and 4-5-6 already in place, the hand would gain 2 fu, but lose 1 han for not scoring pinfu.
, 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. It is limited by needing only one tile type for completion. 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.
Wait strength
The pattern is generally weak in terms of the number of tiles needed for completion. However, the pattern may be strengthened with the use of suji.