Originally Posted by Adraco

Very hard on a RON campaign to project exact costs in real time, your ad might get out on hundreds of pages and suddenly get higher than usual or more than projected clicks and before it all comes back, you might end up a bit over. Not much, but still over. The way I see it, that's just how a RON campaign works. A set spending budget should, however, be "reasonably" repsected, which means a few percent over one day should mean the campaign stops a few percent short the next day, to average out over time when the sample space is large enough.