When dragging an Entry Point object onto the canvas, you must define a Traffic Source. Under "Acquisition Type", there are two options available: Impressions or Clicks.
To use CPM (or Cost per One Thousand Impressions), select "Impressions" from the drop down menu as shown below:
For this example, the values shown above are taken directly from a Facebook ad campaign as shown here:
Using the example numbers from the above FB campaign, GERU displays the number of link clicks (visitors to the Opt-In object) and the Traffic Cost...
NOTE: Due to number rounding, you may notice some minor differences as shown above $282.18 versus $282.08
Here is a breakdown of the CPM math and calculations using the above Facebook & GERU numbers:
$11.81 CPM = $11.81 per 1,000 impressions