<<
How many posts does it take to increase the average by one?
Why is it that the posts per day average seems to fall faster(when not posting) vs how slow it increases(when posting)? >>
Roger is correct on how it's determined.
The impact is a result of:
Number of posts (n) increases your daily post count by n/d, where d is the number of days you've been registered. If you've been here two years 30 posts made in one day would increase your PPD by 30/730 = 0.041 - or practically nothing.
The impact of posting absence varies by the length of time you've been registered. The effect specifically can be represented as previous PPD * (1 - (a/d)), where a is the length of absence & d is the total days registered.
For example...
You've been registered 4 days. The first three days you made 20 posts per day, the fourth day you made none. Total post count is 60.
20 * (1-(1/4)) = 15
If you've been registered 40 days & you miss one day (again assuming 20 posts per day, total post count of 780, 40th day you made none):
20 * (1-(1/40)) = 19.5
Missing a second day would result in:
19.5 * (1-(1/41)) = 19.024390243902439024390243902439
Which just so happens to be the same as:
20 * (1-(2/41)) = 19.024390243902439024390243902439
Viper GTS