You could always hack around with the values and see what happens if you're so inclined. I think the other side of this stuff is done in .Net if you wanted to try and take it apart. I'm not going fishing, I think they're gonna revisit this stuff at some point when they get to it making whatever you do now kind of useless.
I'd assume there's some kind of daily (or timed somehow) function that calls this stuff and processes it, yeah. Not sure of the details.
What does seem obvious is that there's more out than in and when you place a tannery, boom supply demand is met and profit goes up.