unrestricted/no bounderaries CPM(not RPM lol)
Well back in 2009 Machinima had this great idea that in order to get ahead of TGS and Maker, they would promise to pay $1.70 for each 1000 views (fixed rate), At the time this seemed amazing because the average CPM at that time was 1-2 dollars, so that was above average.
Then about a year later Machinima had to step that up to $2.50 because CPMs were rising fast.
Late 2010/early 2011 : Multiple other networks who had fixed CPMs took them away because CPMs were getting so high that fixed was no longer worth it.
9 months ago : Machinima finally took away their fixed CPM contract knowing that it was a dieing trend!
Now : Fixed CPMs are now terrible because with some of the better networks , CPMs can range from $3-$10 meaning that you would have to set the fixed CPM quite high(but then your network would ake a loss) so fixed are smaller amounts than unfixed the only benefit being is that you know you will always get the same amount per 1000 views. (which isn`t really good anymore since the lowest unfixed CPMs go seems to be the value in which most fixed CPM networks pay out...)