Effort per level formula abstracts out the experience curve(or other diminishing returns spending) into a progressive series of additional points to gain.
Reduces grind and provides a smooth expirience of level gain .
It soft caps the effort required at higher levels to manageable portions that are suitable for short-period gameplay(e.g. casual session).

Effort unit=One task, i.e. one average monster(of level equal to player).
Example(log2 formula):
Effort units per level=10*Log2(level*16)
E.g. to reach next level you need 40 effort units=40 monsters of your level to kill.
Example table generator in C:
Table can be viewed at http://videogamedesign.wikidot.com/table:effort-units-per-level

#include <stdio.h>
#include <math.h>
int main(){
for(int i=1;i<1000;i++){printf("\n||%i||%f||",i,10.0*log2((double)(i*16)));}