Koban (coin)
The koban (小判?) was a Japanese oval gold coin in Edo period feudal Japan, equal to one ryō, another early Japanese monetary unit. It was a central part of Tokugawa coinage.
The Keichō era koban, a gold piece, contained about one ryō of gold, so that koban carried a face value of one ryō. However, successive mintings of the koban had varying (usually diminishing) amounts of gold. As a result, the ryō as a unit of weight of gold and the ryō as the face value of the koban were no longer synonymous.
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