The cost per mille standard comes from old-style non-interactive advertising and is not always applicable in digital media. A CPC, or cost-per-click, model has the advertiser pay only when the party that sees the ad clicks on it. CPA, or cost-per-action, ads only require payment when a user takes action. CPM ads are cheaper than CPC ads, which are cheaper than CPA ads, all other things being equal, but they also promise less. For companies that want to get something clear and provable from their ads, the CPC and CPA pricing models may be better choices.