Professional Go Handicaps - Josen

The foundation of the old system was that josen applied to a professional rank difference of 2 dan.

Josen (定先?) is the go term describing the phase in a series of matches between two players - such as a jubango, where one player takes Black (makes the first move) throughout. One says also "playing at sen", or a "one-stone-handicap game".

Players are taken to be evenly matched at two ranks apart if the victories are evenly divided at sen; or in other words the higher-ranked player can manage 50% wins with White.