This tool is simple and fairly precise.
You just need to fill the age of your player, number of doctors you have plus the length of the players injury (for use 0).
As a result you are told how long it will maximum take to heal your player and how long it will minimum take. It of course depends on if he is for example high 1 or low 1. So the most precise you get if you put in the data after a players injury changes eg from 5 to 4 and then it is the maximum time that you should count on.
use 0).
1 or low