QUOTE(Cstro1 @ Apr 21 2016, 10:05)

I don't know why but artifact drop rate is widely different.
One day you get only 4 then another day, you get about 15.
Indeed. That's why in the mechanism in the screenshot, artifacts are estimated rather than checked exactly. It's the same thing with other low-probability drops; mags, legs, chaos tokens, blood tokens, etc. Since the chance of them dropping is so low, it takes many many samples to come up with a good confidence interval that isn't incredibly large.
I started out measuring artifacts exactly but then I came to the same conclusion as you, since the large variation was wrecking the revenue averages.
Luckily, in the case of artifacts, we can calculate their drop chances (almost) exactly... assuming the formula on the wiki is correct (IMG:[
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style_emoticons/default/tongue.gif)
That way there's never any disappointment from "I only got 1 artifact yesterday (IMG:[
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style_emoticons/default/cry.gif)" etc.