The AdSense API earnings report shows aggregated earnings for all ads that contained your developer id which appeared on your publishers' pages. The report is very similar to the earnings report that you see for the regular AdSense program, with one difference. The API report shows ad unit impressions, ad unit CTR (click through rate), and ad unit eCPM instead of impressions, CTR, and eCPM. An "ad unit" is the ad or group of ads that a single AdSense JavaScript code snippet generate. Often an ad unit contains three to five ads.
For each line of this chart, two equations are relevant, one relates impressions and CTR and another relates impressions and eCPM. The relationship between clicks and CTR is defined by
Ad unit CTR = ((Ad unit impressions) / (Clicks)) * 100
The relationship between impressions and eCPM is defined by
Ad unit eCPM = (Earnings) / ((Ad unit impressions) / 1000))
Remember that all numbers are rounded to two decimal places.
Something to keep in mind when looking at eCPM on this report is that the eCPM is post-revenue share. If this developer is keeping 30%, the "total" eCPM is actually $1.10. The aggregate eCPM for this developer's publishers from the API is $0.77, reflecting the 70% of the revenue they are getting.