Why do you like Acashic Record so much?

[tinkthank]

With this question I am implying both that I don't get it and a second question:
Under "normal" site frequency conditions, what are the chances of a site being in any given province?

Back to the main question: AR costs 25 pearls; that means if you find 1 1-pearl site, it will pay for itself in 25 turns. It is hard to quantify what "payoff" means in other terms (how badly do you want earth gems vs. pearls, or other types of gems...?), but let's try. If you find 2 sites, say an 1-earth and a 1-pearl site, it pays for itself in 12 turns.
But I usually play "normal" site frequency maps and even with very decent searchers, I often turn up zero-site provinces. But how often do these occur? Does the "40" in "site frequency setting" mean that there will be a 40% that at least one site will occur? Or is some d6oe going on here?