The coverage rate corresponds to the number of ads where the site is visible compared to the total number of ads present multiplied by 100.
Myposeo analyzes a keyword 10 times, and your site is present twice. On these 7 times, your site normally has only 1 Adwords ad.
The total coverage rate is the average of the coverage rates for the checks on which your site is present (2 in our example). It is 42%.