A janitor presses a block of wood into a disc sander, spraying sawdust everywhere. The janitor then collects and packages the sawdust to be sold. The price is set based on hourly production: however much the janitor can produce and pack in one hour costs $13, minimum wage in San Francisco.
Revenue from sawdust sales is used to pay the janitor. When the wood runs out, the janitor is dismissed from the job.