Network agrees farming rate FR
users pay safecoin to store SS (calculate from FR)
farmers get farmed safecoin FS
so the farmer gets FS at a rate dependent on his rank (say between 0 and 1)
The global FR is calculated like this (not the equation this is elia5)
Get request satisfied by farmer. A random (but deterministic) number is calculated (this is the hash of several items such as message_id requester ID and the ID of all the close group to the farmer) this number is called NUMBER.
So we calculate if(NUMBER % FR == 0) { do farming request (try and get a safecoin)
the % means modulo division so if NUMBER divided by FR has no remainder then a farming request happens. So this is the lottery.