Click the green flag. Use the number sliders. Starting number is the percent you start with. Modifying number is what you want to fairmath add/subtract by Output is what the outcome percent will be. (this will not ever output 100 or 0 unless you start with that number)
The idea of fairmath is that the closer a variable is to 100 (the higher it is), the harder it is to increase, and the closer a variable is to 0 (the lower it is), the harder it is to decrease:
