hi. i got a reply from the author:
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You may think ‘hits’ as ‘clicks’
If a person moves around your blog, ‘hits’ count would increase, but ‘visits’ count won’t increase (by 1).
If a person stop moving around your blog, and after 30 minutes, he start to move another pages on your blog, then ‘visits’ count would increase.
If you want to know about unique visitors(IP), just see ‘unique’ values. (you should set ‘Visit type:’ to ‘unique’ on your slimstat option page)
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?? I understand now! ??