Coal miners shopped for their daily supplies at colliery-owned or affiliated shops.
They made their payment by Tanken, vouchers issued by the colliery company for their salary, instead of cash.
The shops were called Urikanba, and they charged higher prices than shops outside the mine.
In order to make a profit, shrewd head clerks at rice shops would often measure less rice than the miners were actually paying for.
Seeing as Tanken were only valid at the Urikanba, miners had no choice but to give in and accept the amount of rice they were given.