CPM is cost per mille, the advert cost per thousand views. I wanna know how Hubpages Ad Program CPM is working, Why that is varying? Sometimes I will be having very low traffic to my hubs and sometimes it is very high. The worst part is when ever I have very low traffic I get very high CPM of Hubpages Ad Program and when ever the traffic is very high, CPM of Hubpages Ad Program falls drastically. How Hubpages Ad Program CPM works? Why it is varying, how to improve it?