The number everyone quotes
Buying teams still compare screens on CPM because it is the one figure every platform reports the same way. It is also the figure that hides the most.
What a fuller read includes
Attention, completion, incremental reach against the digital plan, and the conversion that follows in the weeks after the spot runs, not the hours after it.
Where the picture changes
Once incremental reach is priced in, linear frequently lands cheaper than the CPM comparison suggests, and some streaming inventory lands dearer.
What to do with it
Set the measurement design before the buy, not after. The plan you can read is worth more than the plan that looked cheapest on paper.