Since we don't have javascript in our ad code and don't spy on visitors, we can't reliably distinguish them. That is why we are not pay-per-click or pay-per-impression network and our default metric is different from the one used in AdSense.

By default we count unique impressions that come from globally unique IPs during a day. According to our global stats, ~1.7% of impressions is unique, our average CPM (based on the unique impressions) is ~0.001 btc. Ad units that attract advertisers may earn much more.

On the stats page of your ad unit you can see non-unique impressions too. E. g. your ad unit #39771 generated ~23K non-unique impressions and your ad unit #39751 generated ~2.4K non-unique impressions. Thus you generated ~25K of impressions in total, 471 of them (~1.8%) are unique, a bit better than average.

But your CPM is several times lower than average. Probably that's due to 2 reasons:
1) your ad units are in the "unknown" category (since they are not present at the specified URLs, they were not categorized by our moderators)
2) you disallow shady ads (that is good for your reputation but bad for earnings since some of our paying advertisers are tagged as "shady").

Please note that all ad units automatically participate in our affiliate program and can earn much more if they accidentally attract advertisers to our service. For example, our own ad unit currently earns most of its money this way (see the red line "Goals" in earnings of https://a-ads.com/ad_units/1/stats).

See also: http://blog.anonymousads.com/2014/08/why-am-i-not-paid-for-clicks-what-is.html