A creative's daily click-through rate against how many times the average person has seen it. The fit reads the level, the onset and the decay off the curve, or says why it cannot. (Synthetic. The four presets are the creatives the post's notebook pins.)
A smaller audience saturates sooner, so exposure climbs faster. A decay of zero is a creative that never tires: every bend the fit reports on it is a false one.
Click-through rate against impressions per person reached
How that axis was built: impressions per person, climbing day by day