What is the only mistake in my original question? “Cost Per Impression” is not “CPM”, as if “M” is a phonetic abbreviation for “impression” That is why the “m” is “thousand”, while “CPM” is “cost per thousand” we are saying that impressions are used for all “impressions”, the “impressions” being implied

In advertising, CPM is typically the billing unit, CPI is rarely if ever used, and this applies to print as well as internet. If you book an advert campaign for your car or scotch to be in every Conde Nast publication in the US, your billing will be based on the total number of magazines sold (or maybe printed, as in the original meaning of “impression”), regardless of the circulation of the individual magazine

titles.