How to use the handicap parameter?

[horaceho]

In @whr.create_game("shusaku", "shusai", "B", 1, handicap), is the handicap

1. the rank differece between the two players (e.g. 1d vs 5d)?
2. or the handicap of game being played (stones on board)?

If both means something similar, what value should be used for the difference (rank difference or stone), for example, 1d (B) vs 5d (W), 4 stones? Should it be 4, or (4 x some weight)?