When scoring a hand, the number of Han (also called Doubles) determines the number of times a hand's
Points are doubled. Learning the Han values is easier than determining a hand's Point value (based on
the number and type of Sets, the difficulty of the Wait, and a few other factors), and is by far the most significant factor determining
the final value of a hand. This fact allows beginners to play a very competitive game just by knowing the Han values, and leaving the
Point calculation to another player at the table (it is very common to see 3 players at a table relying on the 4th player, or the "resident scorekeeper").
There are quite a few hands to remember for Reach Mahjong, but they will become more intuitive as you become accustomed to the patterns. As a general rule, players are rewarded for consistency (for examples, see Flush, Outside and Inside hands, Triple Run, etc.).
For Beginners: If the number of Hands seems overwhelming, try learning the first 6 One-Han hands (on the following list). These are by far the most common hands, and combined with Doras they are often sufficient to compete well with seasoned players. You could even play a game that only allows these 6 hands, for practice purposes.
Han are earned whenever your hand fulfills the conditions for a given hand. This means that different Hands are often combinable. For example, the Inside Hand is a hand that lacks 1s, 9s and Honors (Value=1 Han), and the 3-Closed Sets hand is a hand that contains three unrevealed sets (Value=2 Han). These hands could be combined, as in:
...creating a Hand with a Han value of 3: Inside Hand (1 Han) + 3-Closed Sets (2 Han) = 3 Han. Any number of combinations of Hands are possible due to this mutual inexclusiveness of Hands.
Players are generally rewarded for going out with a Closed Hand (no steals) rather than an Open Hand (one or more steals). Hands are affected by stealing in one of the following ways.
1. Most commonly, Stealing reduces the Han Value of a Hand by 1. Ex: Triple Run goes from 2 Han to 1 Han. Flat Hand goes from 1 Han to 0 (no longer a hand).
2. Stealing makes the Hand have no Han Value. Ex: Double-Double Run.
3. Stealing does not affect the hand. Ex: Inside hand, All Sets, most Limit Hands.
A note on the affect of stealing is included for each Hand on the following list.